Add FLAG_IMMUTABLE to PendingIntents

If your app targets Android 12, you must specify the mutability of each PendingIntent
object that your app creates. This additional requirement improves your app's security.
https://developer.android.com/about/versions/12/behavior-changes-12#pending-intent-mutability

Android Lint is being updated, and adds an error-level check for this.

Bug: 247885568
Test: Presubmits
Change-Id: I2bb91d98b443af2b5c16944ce197d863dbd33f9a
2 files changed