Brightness Slider: changes for extension

Decomposed SystemUI brightness slider and provided DI for related
classes in order to provide functionality to change brightness slider
behavior for Google devices only.

Manual tests:
1. Manually interacted with Google brightness slider and confirm that
   brightness changed accordingly.
2. Changed brightness via `adb` commands and confirmed that brightness
   slider was reacting as expected.
3. Provided the same tests for both QS and Settings brightness slider.
4. Provided Screen Record and confirmed that brightness slider mirror
   original slider behavior.
5. Checked AConfig flag works as expected and provide SystemUI slider
   classes when AConfig flag is disabled.

Bug: 376788704
Flag: EXEMPT refactor

Test: Manual tests
Test: atest com.android.systemui.settings.brightness
Change-Id: Ia4f2ef3272a2110de522df912166f6f46211c1e0