Merge "Mark implicit PendingIntents as immutable" into rvc-dev am: e35ad478 am: 205fd265 am: 0288878d am: 1850989b

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

Change-Id: If556c7f5272017d506b282c2c95b88f0c1ffe4f4