Move transformationSpec and overscrollSpec to Transition

This CL moves transformationSpec and overscrollSpec from STLState to
Transition. This makes more sense given that those are properties of the
current transition, and this will be necessary for b/290930950 given
that multiples transitions will run in parallel in the future.

Bug: 290930950
Test: atest PlatformComposeSceneTransitionLayoutTests
Flag: N/A
Change-Id: I1d5eb40fb5ed079fbf66918c8bccb46af36faf27