Export PATH and ERRNO_CODES from Emscripten. ### Description

Fixes #2577 by exporting `PATH` and `ERRNO_CODES` from Emscripten

### 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- [x] Add new / update outdated documentation

[tool:pytest]
norecursedirs =
    build
    cpython
    emsdk
    .artifacts
addopts =
    --doctest-modules
    --ignore="packages/matplotlib/src"
markers =
    skip_refcount_check: Dont run refcount checks
    skip_pyproxy_check: Dont run pyproxy allocation checks
    driver_timeout: Set script timeout in WebDriver
testpaths =
    src
    pyodide-build
    packages


[bumpversion]
current_version = 0.20.0
commit = False
tag = False
tag_name = {new_version}

[bumpversion:file:src/py/pyodide/__init__.py]
search = __version__ = "{current_version}"
replace = __version__ = "{new_version}"

[bumpversion:file:src/py/setup.cfg]
search = version = {current_version}
replace = version = {new_version}

[bumpversion:file:pyodide-build/setup.cfg]
search = version = {current_version}
replace = version = {new_version}

[bumpversion:file:run_docker]
search = PYODIDE_PREBUILT_IMAGE_TAG="{current_version}"
replace = PYODIDE_PREBUILT_IMAGE_TAG="{new_version}"

[tool:pytest]
norecursedirs =
    build
    cpython
    emsdk
    .artifacts
addopts =
    --doctest-modules
    --ignore="packages/matplotlib/src"
markers =
    skip_refcount_check: Dont run refcount checks
    skip_pyproxy_check: Dont run pyproxy allocation checks
    driver_timeout: Set script timeout in WebDriver
testpaths =
    src
    pyodide-build
    packages


[bumpversion]
current_version = 0.20.0
commit = False
tag = False
tag_name = {new_version}

[bumpversion:file:src/py/pyodide/__init__.py]
search = __version__ = "{current_version}"
replace = __version__ = "{new_version}"

[bumpversion:file:src/py/setup.cfg]
search = version = {current_version}
replace = version = {new_version}

[bumpversion:file:pyodide-build/setup.cfg]
search = version = {current_version}
replace = version = {new_version}

[bumpversion:file:run_docker]
search = PYODIDE_PREBUILT_IMAGE_TAG="{current_version}"
replace = PYODIDE_PREBUILT_IMAGE_TAG="{new_version}"
