Merge "Set FLAG_IMMUTABLE flag on FirstScreenBroadcast PendingIntent." into sc-dev am: ed85ee6ca6

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/14066641

Change-Id: I2aa2db56b4209247af17f41b2e29f22d8094ca63