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- [x] Add new / update outdated documentation

from pyodide_test_runner import run_in_pyodide


@run_in_pyodide(
    packages=[
        "msprime",
    ]
)
def test_msprime():
    import msprime
    import tskit

    # basic test
    ts = msprime.sim_ancestry(10, random_seed=42)
    ts.dump("/tmp/msprime.trees")
    ts = tskit.load("/tmp/msprime.trees")
    ts2 = msprime.sim_ancestry(10, random_seed=42)
    ts.tables.assert_equals(ts2.tables, ignore_provenance=True)

from pyodide_test_runner import run_in_pyodide


@run_in_pyodide(
    packages=[
        "msprime",
    ]
)
def test_msprime():
    import msprime
    import tskit

    # basic test
    ts = msprime.sim_ancestry(10, random_seed=42)
    ts.dump("/tmp/msprime.trees")
    ts = tskit.load("/tmp/msprime.trees")
    ts2 = msprime.sim_ancestry(10, random_seed=42)
    ts.tables.assert_equals(ts2.tables, ignore_provenance=True)
