Allow multiple python interpreters per process

Checklist

• the issue is indeed a bug and not a support request
• issue doesn't already exist: https://github.com/kivy/python-for-android/issues
• I have a short, runnable example that reproduces the issue
• I reproduced the problem with the latest development version (p4a.branch = develop)
• I used the grave accent (aka backticks) to format code or logs when appropriated

Versions

• Python: 3.9
• OS: Linux
• Kivy: N/A
• Cython: N/A
• OpenJDK: 11

Description

Currently the native code starting the python interpreter only handles a single interpreter per process. This limits how applications handle services (and soon workers) as the python interpreter always has to be run in a separate process instead of a separate thread in the current process. This is managed in the AndroidManifest.xml file by declaring android:process in the service declarations.

Python does support this via sub-interpreters, but the setup is more complex. It would be nice to support that, though. Particularly for workers where they currently have to use more complex RemoteListenableWorker class.

Beginne mit pythonforandroid/bootstraps/common/build/jni/application/src/start.c und prüfe, wie das AndroidManifest.xml Dienstprozesse deklariert. Lies die Dokumentation von Python zur Unterstützung von Sub-Interpretern und überlege, wie dies mit Workern und RemoteListenableWorker zusammenhängt. Als erledigt gilt, dass Dienste oder Worker mehrere Python-Interpreter innerhalb eines Prozesses verwenden können, statt separate Prozesse zu erfordern.