Experiment with Firebase Crashlytics and plumb (#336) NDCrash (or JavaNDCrash) to get a hang of native crashes (in firestack) that plague the app (#911).

Firebase Crashlytics (reporting just the crashes) only for Play Store builds which can be disabled / enabled by users on-demand.

• May be redundant with Android Vitals?
• May not work with gomobile since the eats up the stacktrace?
  • runtime: android backtraces do not include go backtrace golang/go#25035

1. firestack-debug.aar is built with symbols unstripped (note that go code's symbols are not stripped regardless of the ldflags at build time).
2. Firebase CLI must be used to upload symbols (ref) as the Firebase Gradle plugin (ex) does not upload symbols from AARs: Document/support AAR-level Crashlytics native symbol generation/upload firebase/firebase-android-sdk#1599
3. Firebase Crashlytics could be enabled/disabled at runtime (ref).