Enable Android Platforms by default for Android-related builds

[katre]

Fixes #16285.

RELNOTES: Enable Platforms and Toolchains for Android. Android projects will need to stop passing the legacy flag --fat_apk_cpu, and instead use --android_platforms using platforms defined with the @platforms//os:android constraint. The https://github.com/bazelbuild/rules_android repository defines four standard Android platforms for projects that use those rules, @rules_android//:armeabi-v7a, @rules_android//:arm64-v8a, @rules_android//:x86, @rules_android//:x86_64.

Blog post describing these changes to follow.

[katre]

Ran downstream tests, identified several types of failures:

• Hard bazel crashes
  • Looks like an NPE in AndroidSdkProvider.getAndroidJar
  • Fix ASAP
  • Bazel
  • rules_jvm_external - examples (Android Robolectric test example)
  • rules_kotlin (Example - Anvil)
  • rules_kotlin (Example - Jetpack Compose)
  • rules_kotlin (Example Bzlmod - Android)
• Project doesn't set --android_platforms but probably should
  • Bazel Examples (android (Android Firebase Cloud Messaging)
  • Bazel Examples (android (Android NDK)
  • Bazel Examples (tutorials (Bazel end-to-end example)
  • rules_android
  • rules_android_ndk
  • rules_foreign_cc (Examples (spawn_strategy=standalone))
  • rules_jvm_external - examples (Android instrumentation test example)
  • rules_jvm_external - examples (Simple example)
  • rules_kotlin (Example - Android)
  • rules_rust (Android Examples)

Next step before submitting this: send fixes for these.

[katre]

Downstream projects are mostly clean at this point. A typical error looks like

'android_library' rule '@bazel_tools//src/tools/android/java/com/google/devtools/build/android/incrementaldeployment:incremental_stub_application' requested an android sdk via toolchain resolution but hasn't set an appropriate --android_platforms value: Either set --noincompatible_enable_android_toolchain_resolution or --android_platforms.

If any more downstream projects fail, assign an issue to me to triage.