MM: Introduce MotionDriver for constraint-driven animations 2/x

This introduces `MotionDriver`, a new component designed to act as a
central manager for driving mechanic-based animations within Compose
hierarchy.

Children now can:
1. Look up the `MotionDriver` from the modifier chain.
2. Request an animated value from it.
3. Supply a reactive `MotionSpec` that defines the animation's behavior.

Test: Tested on the previous MotionValueTests
Bug: 439598401
Flag: com.android.systemui.scene_container
Change-Id: I00f2942c846363c820d43bff24564c86545e2cf6