ENH Support SDL-based packages and add pyxel. ### Description

This adds SDL-based package support to Pyodide and adds pyxel as a PoC. Most of the troubleshooting is done by @kitao and pyxel devs, a big thanks to them.

This is on top of #3505

1) I linked only js part of SDL libraries to the main module and linked the native parts to the side module. So the size increase of the main module is small enough (~0.1MB increase to the pyodide.asm.js).

Before (in #3505):

```
5145705 pyodide.asm.data
1204075 pyodide.asm.js
8862216 pyodide.asm.wasm
```

After:

```
5145705 pyodide.asm.data
1346524 pyodide.asm.js
8905514 pyodide.asm.wasm
```

2) Emscripten draws everything into `Module.canvas`, but the canvas attribute is not set automatically (which makes sense as we don't output any HTML), so it is the user's job to set it manually.

For now, I am thinking of just mentioning it in the FAQ entry, "you need to set pyodide._module.canvas = ...". But it would be probably nice to have an API to set canvas, as pyodide._module is a private attribute.

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

### Demo

https://ryanking13.github.io/pyodide-pyxel-test

(mostly borrowed from the pyxel repository: https://github.com/kitao/pyxel/tree/main/wasm)

#! /usr/bin/env python
# flake8: noqa

# setup: pass
# run: pystone()

"""
"PYSTONE" Benchmark Program

Version:        Python/1.1 (corresponds to C/1.1 plus 2 Pystone fixes)

Author:         Reinhold P. Weicker,  CACM Vol 27, No 10, 10/84 pg. 1013.

                Translated from ADA to C by Rick Richardson.
                Every method to preserve ADA-likeness has been used,
                at the expense of C-ness.

                Translated from C to Python by Guido van Rossum.

Version History:
                Fix Python 3.8 compatibility by replacing time.clock
                with time.perf_counter

                Inofficial version 1.1.1 by Chris Arndt:

                - Make it run under Python 2 and 3 by using
                  "from __future__ import print_function".
                - Change interpreter name in shebang line to plain
                  "python".
                - Add source code encoding declaration.

                Version 1.1 corrects two bugs in version 1.0:

                First, it leaked memory: in Proc1(), NextRecord ends
                up having a pointer to itself.  I have corrected this
                by zapping NextRecord.PtrComp at the end of Proc1().

                Second, Proc3() used the operator != to compare a
                record to None.  This is rather inefficient and not
                true to the intention of the original benchmark (where
                a pointer comparison to None is intended; the !=
                operator attempts to find a method __cmp__ to do value
                comparison of the record).  Version 1.1 runs 5-10
                percent faster than version 1.0, so benchmark figures
                of different versions can't be compared directly.

"""


LOOPS = 50000

from time import perf_counter

__version__ = "1.1.1"

[Ident1, Ident2, Ident3, Ident4, Ident5] = range(1, 6)


class Record:
    def __init__(self, PtrComp=None, Discr=0, EnumComp=0, IntComp=0, StringComp=0):
        self.PtrComp = PtrComp
        self.Discr = Discr
        self.EnumComp = EnumComp
        self.IntComp = IntComp
        self.StringComp = StringComp

    def copy(self):
        return Record(
            self.PtrComp, self.Discr, self.EnumComp, self.IntComp, self.StringComp
        )


TRUE = 1
FALSE = 0


def main(loops=LOOPS):
    benchtime, stones = pystones(loops)
    print("%g" % benchtime)


def pystones(loops=LOOPS):
    return Proc0(loops)


IntGlob = 0
BoolGlob = FALSE
Char1Glob = "\0"
Char2Glob = "\0"
Array1Glob = [0] * 51
Array2Glob = [x[:] for x in [Array1Glob] * 51]
PtrGlb = None
PtrGlbNext = None


def Proc0(loops=LOOPS):
    global IntGlob
    global BoolGlob
    global Char1Glob
    global Char2Glob
    global Array1Glob
    global Array2Glob
    global PtrGlb
    global PtrGlbNext

    starttime = perf_counter()
    for i in range(loops):
        pass
    nulltime = perf_counter() - starttime

    PtrGlbNext = Record()
    PtrGlb = Record()
    PtrGlb.PtrComp = PtrGlbNext
    PtrGlb.Discr = Ident1
    PtrGlb.EnumComp = Ident3
    PtrGlb.IntComp = 40
    PtrGlb.StringComp = "DHRYSTONE PROGRAM, SOME STRING"
    String1Loc = "DHRYSTONE PROGRAM, 1'ST STRING"
    Array2Glob[8][7] = 10

    starttime = perf_counter()

    for i in range(loops):
        Proc5()
        Proc4()
        IntLoc1 = 2
        IntLoc2 = 3
        String2Loc = "DHRYSTONE PROGRAM, 2'ND STRING"
        EnumLoc = Ident2
        BoolGlob = not Func2(String1Loc, String2Loc)
        while IntLoc1 < IntLoc2:
            IntLoc3 = 5 * IntLoc1 - IntLoc2
            IntLoc3 = Proc7(IntLoc1, IntLoc2)
            IntLoc1 = IntLoc1 + 1
        Proc8(Array1Glob, Array2Glob, IntLoc1, IntLoc3)
        PtrGlb = Proc1(PtrGlb)
        CharIndex = "A"
        while CharIndex <= Char2Glob:
            if EnumLoc == Func1(CharIndex, "C"):
                EnumLoc = Proc6(Ident1)
            CharIndex = chr(ord(CharIndex) + 1)
        IntLoc3 = IntLoc2 * IntLoc1
        IntLoc2 = IntLoc3 / IntLoc1
        IntLoc2 = 7 * (IntLoc3 - IntLoc2) - IntLoc1
        IntLoc1 = Proc2(IntLoc1)

    benchtime = perf_counter() - starttime - nulltime
    if benchtime == 0.0:
        loopsPerBenchtime = 0.0
    else:
        loopsPerBenchtime = loops / benchtime
    return benchtime, loopsPerBenchtime


def Proc1(PtrParIn):
    PtrParIn.PtrComp = NextRecord = PtrGlb.copy()
    PtrParIn.IntComp = 5
    NextRecord.IntComp = PtrParIn.IntComp
    NextRecord.PtrComp = PtrParIn.PtrComp
    NextRecord.PtrComp = Proc3(NextRecord.PtrComp)
    if NextRecord.Discr == Ident1:
        NextRecord.IntComp = 6
        NextRecord.EnumComp = Proc6(PtrParIn.EnumComp)
        NextRecord.PtrComp = PtrGlb.PtrComp
        NextRecord.IntComp = Proc7(NextRecord.IntComp, 10)
    else:
        PtrParIn = NextRecord.copy()
    NextRecord.PtrComp = None
    return PtrParIn


def Proc2(IntParIO):
    IntLoc = IntParIO + 10
    while 1:
        if Char1Glob == "A":
            IntLoc = IntLoc - 1
            IntParIO = IntLoc - IntGlob
            EnumLoc = Ident1
        if EnumLoc == Ident1:
            break
    return IntParIO


def Proc3(PtrParOut):
    global IntGlob

    if PtrGlb is not None:
        PtrParOut = PtrGlb.PtrComp
    else:
        IntGlob = 100
    PtrGlb.IntComp = Proc7(10, IntGlob)
    return PtrParOut


def Proc4():
    global Char2Glob

    BoolLoc = Char1Glob == "A"
    BoolLoc = BoolLoc or BoolGlob
    Char2Glob = "B"


def Proc5():
    global Char1Glob
    global BoolGlob

    Char1Glob = "A"
    BoolGlob = FALSE


def Proc6(EnumParIn):
    EnumParOut = EnumParIn
    if not Func3(EnumParIn):
        EnumParOut = Ident4
    if EnumParIn == Ident1:
        EnumParOut = Ident1
    elif EnumParIn == Ident2:
        if IntGlob > 100:
            EnumParOut = Ident1
        else:
            EnumParOut = Ident4
    elif EnumParIn == Ident3:
        EnumParOut = Ident2
    elif EnumParIn == Ident4:
        pass
    elif EnumParIn == Ident5:
        EnumParOut = Ident3
    return EnumParOut


def Proc7(IntParI1, IntParI2):
    IntLoc = IntParI1 + 2
    IntParOut = IntParI2 + IntLoc
    return IntParOut


def Proc8(Array1Par, Array2Par, IntParI1, IntParI2):
    global IntGlob

    IntLoc = IntParI1 + 5
    Array1Par[IntLoc] = IntParI2
    Array1Par[IntLoc + 1] = Array1Par[IntLoc]
    Array1Par[IntLoc + 30] = IntLoc
    for IntIndex in range(IntLoc, IntLoc + 2):
        Array2Par[IntLoc][IntIndex] = IntLoc
    Array2Par[IntLoc][IntLoc - 1] = Array2Par[IntLoc][IntLoc - 1] + 1
    Array2Par[IntLoc + 20][IntLoc] = Array1Par[IntLoc]
    IntGlob = 5


def Func1(CharPar1, CharPar2):
    CharLoc1 = CharPar1
    CharLoc2 = CharLoc1
    if CharLoc2 != CharPar2:
        return Ident1
    else:
        return Ident2


def Func2(StrParI1, StrParI2):
    IntLoc = 1
    while IntLoc <= 1:
        if Func1(StrParI1[IntLoc], StrParI2[IntLoc + 1]) == Ident1:
            CharLoc = "A"
            IntLoc = IntLoc + 1
    if CharLoc >= "W" and CharLoc <= "Z":
        IntLoc = 7
    if CharLoc == "X":
        return TRUE
    else:
        if StrParI1 > StrParI2:
            IntLoc = IntLoc + 7
            return TRUE
        else:
            return FALSE


def Func3(EnumParIn):
    EnumLoc = EnumParIn
    if EnumLoc == Ident3:
        return TRUE
    return FALSE


def pystone():
    main(LOOPS)

#! /usr/bin/env python
# flake8: noqa

# setup: pass
# run: pystone()

"""
"PYSTONE" Benchmark Program

Version:        Python/1.1 (corresponds to C/1.1 plus 2 Pystone fixes)

Author:         Reinhold P. Weicker,  CACM Vol 27, No 10, 10/84 pg. 1013.

                Translated from ADA to C by Rick Richardson.
                Every method to preserve ADA-likeness has been used,
                at the expense of C-ness.

                Translated from C to Python by Guido van Rossum.

Version History:
                Fix Python 3.8 compatibility by replacing time.clock
                with time.perf_counter

                Inofficial version 1.1.1 by Chris Arndt:

                - Make it run under Python 2 and 3 by using
                  "from __future__ import print_function".
                - Change interpreter name in shebang line to plain
                  "python".
                - Add source code encoding declaration.

                Version 1.1 corrects two bugs in version 1.0:

                First, it leaked memory: in Proc1(), NextRecord ends
                up having a pointer to itself.  I have corrected this
                by zapping NextRecord.PtrComp at the end of Proc1().

                Second, Proc3() used the operator != to compare a
                record to None.  This is rather inefficient and not
                true to the intention of the original benchmark (where
                a pointer comparison to None is intended; the !=
                operator attempts to find a method __cmp__ to do value
                comparison of the record).  Version 1.1 runs 5-10
                percent faster than version 1.0, so benchmark figures
                of different versions can't be compared directly.

"""


LOOPS = 50000

from time import perf_counter

__version__ = "1.1.1"

[Ident1, Ident2, Ident3, Ident4, Ident5] = range(1, 6)


class Record:
    def __init__(self, PtrComp=None, Discr=0, EnumComp=0, IntComp=0, StringComp=0):
        self.PtrComp = PtrComp
        self.Discr = Discr
        self.EnumComp = EnumComp
        self.IntComp = IntComp
        self.StringComp = StringComp

    def copy(self):
        return Record(
            self.PtrComp, self.Discr, self.EnumComp, self.IntComp, self.StringComp
        )


TRUE = 1
FALSE = 0


def main(loops=LOOPS):
    benchtime, stones = pystones(loops)
    print("%g" % benchtime)


def pystones(loops=LOOPS):
    return Proc0(loops)


IntGlob = 0
BoolGlob = FALSE
Char1Glob = "\0"
Char2Glob = "\0"
Array1Glob = [0] * 51
Array2Glob = [x[:] for x in [Array1Glob] * 51]
PtrGlb = None
PtrGlbNext = None


def Proc0(loops=LOOPS):
    global IntGlob
    global BoolGlob
    global Char1Glob
    global Char2Glob
    global Array1Glob
    global Array2Glob
    global PtrGlb
    global PtrGlbNext

    starttime = perf_counter()
    for i in range(loops):
        pass
    nulltime = perf_counter() - starttime

    PtrGlbNext = Record()
    PtrGlb = Record()
    PtrGlb.PtrComp = PtrGlbNext
    PtrGlb.Discr = Ident1
    PtrGlb.EnumComp = Ident3
    PtrGlb.IntComp = 40
    PtrGlb.StringComp = "DHRYSTONE PROGRAM, SOME STRING"
    String1Loc = "DHRYSTONE PROGRAM, 1'ST STRING"
    Array2Glob[8][7] = 10

    starttime = perf_counter()

    for i in range(loops):
        Proc5()
        Proc4()
        IntLoc1 = 2
        IntLoc2 = 3
        String2Loc = "DHRYSTONE PROGRAM, 2'ND STRING"
        EnumLoc = Ident2
        BoolGlob = not Func2(String1Loc, String2Loc)
        while IntLoc1 < IntLoc2:
            IntLoc3 = 5 * IntLoc1 - IntLoc2
            IntLoc3 = Proc7(IntLoc1, IntLoc2)
            IntLoc1 = IntLoc1 + 1
        Proc8(Array1Glob, Array2Glob, IntLoc1, IntLoc3)
        PtrGlb = Proc1(PtrGlb)
        CharIndex = "A"
        while CharIndex <= Char2Glob:
            if EnumLoc == Func1(CharIndex, "C"):
                EnumLoc = Proc6(Ident1)
            CharIndex = chr(ord(CharIndex) + 1)
        IntLoc3 = IntLoc2 * IntLoc1
        IntLoc2 = IntLoc3 / IntLoc1
        IntLoc2 = 7 * (IntLoc3 - IntLoc2) - IntLoc1
        IntLoc1 = Proc2(IntLoc1)

    benchtime = perf_counter() - starttime - nulltime
    if benchtime == 0.0:
        loopsPerBenchtime = 0.0
    else:
        loopsPerBenchtime = loops / benchtime
    return benchtime, loopsPerBenchtime


def Proc1(PtrParIn):
    PtrParIn.PtrComp = NextRecord = PtrGlb.copy()
    PtrParIn.IntComp = 5
    NextRecord.IntComp = PtrParIn.IntComp
    NextRecord.PtrComp = PtrParIn.PtrComp
    NextRecord.PtrComp = Proc3(NextRecord.PtrComp)
    if NextRecord.Discr == Ident1:
        NextRecord.IntComp = 6
        NextRecord.EnumComp = Proc6(PtrParIn.EnumComp)
        NextRecord.PtrComp = PtrGlb.PtrComp
        NextRecord.IntComp = Proc7(NextRecord.IntComp, 10)
    else:
        PtrParIn = NextRecord.copy()
    NextRecord.PtrComp = None
    return PtrParIn


def Proc2(IntParIO):
    IntLoc = IntParIO + 10
    while 1:
        if Char1Glob == "A":
            IntLoc = IntLoc - 1
            IntParIO = IntLoc - IntGlob
            EnumLoc = Ident1
        if EnumLoc == Ident1:
            break
    return IntParIO


def Proc3(PtrParOut):
    global IntGlob

    if PtrGlb is not None:
        PtrParOut = PtrGlb.PtrComp
    else:
        IntGlob = 100
    PtrGlb.IntComp = Proc7(10, IntGlob)
    return PtrParOut


def Proc4():
    global Char2Glob

    BoolLoc = Char1Glob == "A"
    BoolLoc = BoolLoc or BoolGlob
    Char2Glob = "B"


def Proc5():
    global Char1Glob
    global BoolGlob

    Char1Glob = "A"
    BoolGlob = FALSE


def Proc6(EnumParIn):
    EnumParOut = EnumParIn
    if not Func3(EnumParIn):
        EnumParOut = Ident4
    if EnumParIn == Ident1:
        EnumParOut = Ident1
    elif EnumParIn == Ident2:
        if IntGlob > 100:
            EnumParOut = Ident1
        else:
            EnumParOut = Ident4
    elif EnumParIn == Ident3:
        EnumParOut = Ident2
    elif EnumParIn == Ident4:
        pass
    elif EnumParIn == Ident5:
        EnumParOut = Ident3
    return EnumParOut


def Proc7(IntParI1, IntParI2):
    IntLoc = IntParI1 + 2
    IntParOut = IntParI2 + IntLoc
    return IntParOut


def Proc8(Array1Par, Array2Par, IntParI1, IntParI2):
    global IntGlob

    IntLoc = IntParI1 + 5
    Array1Par[IntLoc] = IntParI2
    Array1Par[IntLoc + 1] = Array1Par[IntLoc]
    Array1Par[IntLoc + 30] = IntLoc
    for IntIndex in range(IntLoc, IntLoc + 2):
        Array2Par[IntLoc][IntIndex] = IntLoc
    Array2Par[IntLoc][IntLoc - 1] = Array2Par[IntLoc][IntLoc - 1] + 1
    Array2Par[IntLoc + 20][IntLoc] = Array1Par[IntLoc]
    IntGlob = 5


def Func1(CharPar1, CharPar2):
    CharLoc1 = CharPar1
    CharLoc2 = CharLoc1
    if CharLoc2 != CharPar2:
        return Ident1
    else:
        return Ident2


def Func2(StrParI1, StrParI2):
    IntLoc = 1
    while IntLoc <= 1:
        if Func1(StrParI1[IntLoc], StrParI2[IntLoc + 1]) == Ident1:
            CharLoc = "A"
            IntLoc = IntLoc + 1
    if CharLoc >= "W" and CharLoc <= "Z":
        IntLoc = 7
    if CharLoc == "X":
        return TRUE
    else:
        if StrParI1 > StrParI2:
            IntLoc = IntLoc + 7
            return TRUE
        else:
            return FALSE


def Func3(EnumParIn):
    EnumLoc = EnumParIn
    if EnumLoc == Ident3:
        return TRUE
    return FALSE


def pystone():
    main(LOOPS)
