[automerger skipped] [DO NOT MERGE] Make GlobalScreenshot PendingIntents immutable am: bb4bfcc575 -s ours am: 57f5463b2a am: 5f3cb8f6e2 am: 4de3723c60

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

Change-Id: Ie28720ae9e53f7e8dd58d12782a562f3adecbc84