Moving BrightnessSettings access out of DisplayBrightnessController.mLock

Bug: b/414297026
Test: manual testing
Flag: EXEMPT bugfix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a394205eef979fa92abe439bfc89e0dc6325a50c)
Merged-In: Ifc41e01fbfa2e117fbd583c4fba29a74eac539ae
Change-Id: Ifc41e01fbfa2e117fbd583c4fba29a74eac539ae
1 file changed