CI: run the tests in an Android emulator

[finagolfin]

I have been cross-compiling and running the tests for this package in my Android CI for a long time- currently building and testing this repo for six different Android API levels- and the official swiftlang workflows now support easily running the cross-compiled tests in an Android emulator.

There are only two problems with adding that official workflow here:

• this repo doesn't use the official workflows to build and test, and there appear to be plans to unify the two sets of workflows.
• I currently have to patch this repo a little to pass on my Android CI, mostly working around tests using local #filePaths and disabling some failing tests.

It would be good to add CI testing using the official Android workflow here, just let me know how you'd like to proceed.

[rnro]

Thanks for raising this - I think this is a good improvement to test coverage. We'll have to look at how much work it would require to run the emulator and I'm also a little reluctant to disable test.

[finagolfin]

Neither are run here now, so both would be an improvement, ie even with a couple disabled.