Settings should store unthrottled brightness

In case of manual brightness, when throttled state is stored user set brightness is lost.
When conditions are back to normal, original brightness state is not restored.

Bug: b/403303379, b/356777411
Test: atest DisplayBrightnessControllerTest, atest DisplayPowerControllerTest,  maual testing, see bug comments
Flag: EXEMPT bugfix
Change-Id: I3507846a04ec5326f958211cace52f4e85ae38c3