Android cibuildwheel support

[mhsmith]

Feature or enhancement

Proposal:

This issue will link together a number of PRs required to support running cibuildwheel for Android. Specifically, we need the following features:

• Produce a release package containing a pre-compiled Python for Android.
• Enable the testbed app to run arbitrary tests on third-party packages.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Linked PRs

• gh-131531: Add android.py package command #131532

[freakboy3742]

For the benefit of other observers - this work will mostly be a reorganisation of pieces of the Android build that either already exist, in service of making those parts easier to use for building and testing third-party packages. It's directly analogous to the changes that have been made recently to the iOS testbed to make it a useful for running third-party test suites.