[automerger skipped] [DO NOT MERGE] Make GlobalScreenshot PendingIntents immutable am: f4eefc55 am: 4cccd0c4 -s ours am: 67bd3cae am: 2170554e am: 6fcec5e8

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/12773073

Change-Id: Ie50da89fa991317fd4a0992b1ea3e2c09d19cb32