Add enable_android_sdk_checks option for Android emulator testing

[marcprux]

The Android CI added in #172 will build against the Swift SDK for Android using the scripts/install-and-build-with-sdk.sh support for building with cross-compilation SDKs, but it does't actually test the package. This PR adds a scripts/android/android-emulator-tests.sh script that will install and configure an Android emulator and then transfer the test cases over to it and run the tests on the emulator.

Notes:

• In addition to the build-only enable_android_sdk_build input to workflows/swift_package_test.yml, we now have an enable_android_sdk_checks boolean which will additionally run a package's test cases.
• The Android emulator requires KVM to be enabled for acceleration, which is not possible in a nested docker container. I saw no reason why the SDK build needs to take place in a nested container, so I moved it to run on the top-level ubuntu-latest container.
• The emulator will only run on x86_64; since we support building against multiple triples (currently defaulting to aarch64-unknown-linux-android28 and x86_64-unknown-linux-android28 in workflows/swift_package_test.yml), we will still build against each of these archs, but only test against x86_64.
• As mentioned previously (Add Android emulator testing to workflow #179 (comment)), not all package testing will pass out of the box, since some tests rely on hardcoded #filePath references to test data (e.g., in swift-crypto), which will not work when the tests are run in an emulator with a separate filesystem. I expect that some of these packages will need to be updated if we are to enable enable_android_sdk_checks for them.

A successful run can be seen at https://github.com/swift-android-sdk/github-workflows/actions/runs/20244304679/job/58120240667

Closes #179 and #83

CC: @finagolfin, @justice-adams-apple, @etcwilde, @shahmishal