[android] run tests on arm64 emulator in CI

[andrurogerz]

By using a slightly outdated version of the Android emulator (see https://issuetracker.google.com/u/1/issues/373790939) and passing some extra flags to qemu (-machine virt, -cpu max), it is possible to run an Android arm64-v8a guest on an x86_64 host on an GitHub runner.

Enabling some arm tests in CI would greatly improve our confidence in ds2 functionality on Android devices. Because arm emulation is slower, we won't want to run the full set of lldb tests on every pull request.