[flexiglass] Integrates Content Dynamics Framework.

Adds a call to SceneTransitionLayout to SceneContainer.
- Transitions remain empty, defaulting to a snap between scenes.
- Because our code is not yet allowed to have hard dependencies on
  anything behind the useCompose build-time flag, we continue to use our
  own version of SceneKey, SceneModel, and UserAction - all of which
  would be replaced by their scene transition analogues in upcoming
  work.

Bug: 280880714
Test: Manually verified navigation through up/down swiping and back
gesture all work as intended.

Change-Id: Ic547b00f33a21d3253b965658052dd6215490219