[android] Bump Target SDK to 31 and patch react-native-firebase

Summary:
The Google Play Store no longer allows uploading bundles for which Target SDK <= 30. This diff:

1. Bumps the Target SDK to 31
2. Makes required changes to AndroidManifest.xml to support SDK v31
3. Includes patch from @ashoat to ensure that react-native-firebase continues to work as expected (see below)

From @ashoat's commit (https://github.com/CommE2E/comm/commit/19c0e0a2f114c12dea19ae6512a86add1a03690f):

Patch react-native-firebase to specify PendingIntent.FLAG_MUTABLE

Android notifs weren't working and I was seeing this error: https://gist.github.com/Ashoat/62cf37d7b180798cf63555660c8a84a8

This was triggering because we had just started targeting SDK 31. I solved it by specifying FLAG_MUTABLE to match behavior from old version of Android. More details here.

Test Plan:

1. See if the AAB uploads properly
2. Debug/Release Android build continue working as expected on Android Emulator

Reviewers: ashoat, tomek, marcin, bartek

Reviewed By: ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5704