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

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

Change-Id: Ice22f1c0952477bfe267fbccc1e033ad014085db