[Refactor] Allow callers to specify volume slider's dimensions

With this CL, VolumeSlider accepts an additional parameter that
specifies the dimensions, such as the thumb height and the thumb width.
This parameter uses the current dimensions by default.

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

Bug:441486377
Flag:EXEMPT PURE_REFACTOR
Test:VolumeSliderScreenshotTest
Change-Id: I21273fcb3a20b7a85701a1881e679903faff2218