Update bootanim theme flag on ui_night_mode change

persist.sys.theme should always be consistent with ui_night_mode
Fixes bug where persist.sys.theme wasn't retained after
restoring from another device.

Test: atest google/perf/boottime/boottime-test -v
Fixes: 139301893
Change-Id: Ib923a483f0817aa6a75d407bd09c32b960083146
Merged-In: Ib923a483f0817aa6a75d407bd09c32b960083146
(cherry picked from commit 4f2ff8e9)