Revert "Revert "Icon: make Icon's Bitmaps immutable""

This reverts commit 8fd35436faeee6968dbd1509c118706f34017db9.

Reason for revert: NotificationTemplateTest fixed
Test: atest CtsAppTestCases:android.app.cts.NotificationTemplateTest
Bug: 227920378

Change-Id: I61dc3cb7620d64a55deb669cb1f08f4676d36456
1 file changed