Add SceneScope.nestedScrollToScene() modifier

Defines the behavior to use when the scrollable element can no longer
handle scroll events, and the conditions under which these events can be
 used to transition to the next scene.

 Also in this CL:
- GestureHandler has been removed, it is no longer needed.
- Overscroll can change the scene based on four configurations:
DuringTransitionBetweenScenes, EdgeNoOverscroll, EdgeWithOverscroll, or
Always.
- Simplified SceneNestedScrollHandler (it is no longer necessary to
define the priorityScene since the connection is reset when the scene
changes).

Test: atest SceneGestureHandlerTest
Bug: 291053278
Flag: NA
Change-Id: Ia4874bff4bdca0a9628d77a3a04c58ee86de47e0