BLD Add DISTDIR variable. ### Description

Adds `DISTDIR` env variable that points to the directory where libraries should be copied to when building shared libraries with recipe.

### Checklists

- [x] Add new / update outdated documentation

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["sharedlib-test-py"])
def test_sharedlib(selenium):
    from sharedlib_test import do_the_thing

    assert do_the_thing(4, 5) == 29

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["sharedlib-test-py"])
def test_sharedlib(selenium):
    from sharedlib_test import do_the_thing

    assert do_the_thing(4, 5) == 29
