Merge "Mark implicit PendingIntents as immutable" into rvc-dev am: e35ad478dc am: 205fd265d0 am: 94b589ba46

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12296407

Change-Id: I2b3a2ae8b5889fa1a8d6d6e656fc0536fbc09e29