[Dock Defend] Add an optional shield to the status bar battery drawable.

The shield will be displayed when the battery is marked as overheated.

Bug: 255625888
Test: manual: issue `adb shell am broadcast -a com.android.systemui.demo
-e command battery -e overheated true` and verify the battery icon
displays a shield
Test: See bug for manual demo video
Test: statusbar.battery tests

Change-Id: I6b3036ae47ad7b5ae8dc78f83d019130935c9b50