Modifies the test runner script to no longer export the the HOST environment
variable, and to allow for tests that produce no Python output (output from the
Android console is still expected and required). These changes stem from
knowledge gained during developing a PR for Android support in cibuildwheel.

Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Loïc Simon <loic.pano@gmail.com>
Co-authored-by: pauleveritt <pauleveritt@me.com>

Basic support for pyrepl in Emscripten. Limitations:
* requires JSPI
* no signal handling implemented

As followup work, it would be nice to implement a webworker variant
for when JSPI is not available and proper signal handling.

Because it requires JSPI, it doesn't work in Safari. Firefox requires
setting an experimental flag. All the Chromiums have full support since
May. Until we make it work without JSPI, let's keep the original web_example
around.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Éric <merwok@netwok.org>