Merge the 2021-09-05 SPL branch from AOSP-Partner

* security-aosp-pi-release:
  Forward fix for: Set FLAG_IMMUTABLE flag on FirstScreenBroadcast PendingIntent.
  Set FLAG_IMMUTABLE flag on FirstScreenBroadcast PendingIntent.

Change-Id: I450c647630378b8c2de21cdb3bb4b354b491233a