react-native-firebase

chore(e2e): ios sim log change, android emu TZ/cpus, longer mocha timeout (#4120)

* chore(e2e): fix android emu timezone, extend mocha timeout

* chore(e2e): abstract android emulator commands, allow 2 cores

* chore(e2e): pre-fetch bundle on iOS, don't pre-boot iOS

pre-booting iOS caused a new flake where detox testee never posted ready to proxy

* chore(e2e): get Xcode dir dynamically for detox framework cache

This allows us to just track virtualized environment upgrades passively,
they appear to update Xcode pretty quickly, and Xcode 12 is coming, so
we will just get that automatically now