Introducing Slider Tracker components for sliders in SysUI.

Components related to the state machine of a slider are introduced.
These include a SliderTracker, SliderState and the concrete
implementation of a tracker for the brightness slider in the system UI
(SeekableSliderTracker).

Test: atest SeekableSliderTrackerTest
Bug: 295932558
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b2e4731cc439095c07ef9de06b612aa14f67efe1)

Change-Id: I04a3d3d38a9f43e7262ff419b183b1cb40177675