Make it possible to compute the swipe distance lazily

This CL makes it possible to compute the swipe distance of swipes
lazily, so that the distance can depend on the size or position of
elements from the scene we are transitioning to.

The way it works is pretty simple: UserActionDistance.absoluteDistance
can return 0f until the swipe distance can be computed. This CL also
exposes a UserActionDistanceScope to get the target size and offset of
an element inside a scene, which are usually useful to compute swipe
distances that depend on an element target state.

Note that some of the code in this CL is going to be moved in
ag/26316632.

Bug: 308961608
Test: SwipeToSceneTest
Flag: N/A
Change-Id: If70c48de0aba7a793942badcb5a24993277302b1