Make WallpaperMS bind wallpaper component PendingIntent immutable.

Require that the PendingIntent be immutable so that a malicious app is
not able to hijack and mutate any of the details.

Fixes: 154915372
Test: build & flash, change wallpaper manually.
Change-Id: I59b48811b26736bf0575769107dd940ca33ccf8d
(cherry picked from commit d4bd69cef05d379555418a8fe748ec94ff6bd6d0)
1 file changed