Mark implicit PendingIntents as immutable am: 504e7d84 am: 46387fb1 am:...

Mark implicit PendingIntents as immutable am: 504e7d84 am: 46387fb1 am: 78c2d2ca am: b0e7b885 am: c7bb9ba8 am: e5d90630 am: 4d38a90b am: 2c7ffc65

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12296465

Change-Id: I5eed6d672215d0e2a40e5982985cb021981b3190