Add support for runtime Python version 3.13

[mhsmith]

Checklist in target/README.md.

This is the first version to have official Android support upstream, so we'll have to work out how to use that while still supporting older versions. Related:

• Problem building Python 3.12 #1143
• Update to newest runtime Python versions (2024) #1211

It's also the first version to have sys.platform == 'android', though I'm not sure if that will affect the Chaquopy runtime.

All Python versions should now use the supporting libraries from cpython-android-source-deps.

[mhsmith]

If necessary, include patches from PRs which aren't included in whatever version we build.