This lets us stop hardcoding platforms and start filtering for which
archives have sources, which is the most accurate way to do it.
Tested on x86_64-linux, aarch64-linux, and aarch64-darwin.
We can figure out the latest version for every package in mkrepo.rb,
instead of repeating ourselves in compose-android-packages.
Track the latest non-preview versions of all packages by default, and
remove version hardcoding everywhere. Enable the update script.
androidenv: apply numinit patch to have a nice error message
androidenv handle unsupported systems, and make tests running by default!
androidenv run nixfmt
androidenv: support emulator/systemimages/NDK only for certain systems
androidenv: apply nixfmt
androidenv: give a warning if archive doesn't exist
