[automerger skipped] [DO NOT MERGE] Make GlobalScreenshot PendingIntents immutable am: bb4bfcc575 -s ours am: 57f5463b2a

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12770654

Change-Id: I7e8b01067a005fde99f79e640b136a6884b85313