Add hereditary option to as_object_map. This automatically apply as_object_map to the values of the map when the values are "plain old objects".

This behavior is slightly naive but I think it will satisfy most people who have requested this feature.


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- [x] Add new / update outdated documentation

import pytest
from pytest_pyodide import run_in_pyodide


@pytest.mark.driver_timeout(60)
@run_in_pyodide(packages=["xarray"])
def test_xarray(selenium):
    import xarray as xr

    da = xr.DataArray(data=[[0, 1, 2], [3, 4, 5]], dims=("x", "y"))
    xr.testing.assert_equal(a=da.mean(), b=xr.DataArray(data=2.5))

import pytest
from pytest_pyodide import run_in_pyodide


@pytest.mark.driver_timeout(60)
@run_in_pyodide(packages=["xarray"])
def test_xarray(selenium):
    import xarray as xr

    da = xr.DataArray(data=[[0, 1, 2], [3, 4, 5]], dims=("x", "y"))
    xr.testing.assert_equal(a=da.mean(), b=xr.DataArray(data=2.5))
