[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: Id8c55a0707285306f9d92aff6ae2c8eabdf32aa1