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

am skip reason: subject contains skip directive

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

Change-Id: I9499cd66f5931b8c853e6a3af64230efcbf764ad