[DO NOT MERGE] Make GlobalScreenshot PendingIntents immutable

Mutable pending intents are a security risk. This change adds the
IMMUTABLE flag to all PendingIntents created in GlobalScreenshot.

Bug: 162738636
Test: manual
Change-Id: I1044b6aaf2b1650ff91d9a72181684d2aaea9a62
(cherry picked from commit ed450d77edc632bbdf74f86fa76dae1f9475a5c9)
1 file changed