Introduce sizing tokens to the QS shade brightness bar

This CL reads the following UI dimens from res, instead of using
hardcoded constants:

1. The thumb height
2. The thumb width
3. The track height

This CL also verifies the slider's height through compose testing. Due
to the merged descendants of the Material 3 slider, only the slider's
height is able to verify.

This CL should not bring any UI differences to the product.

Bug: 427487608
Flag: EXEMPT refactor
Change-Id: Id8fe63bae4adbae56c0f73336ebb64aa26179dc4