Optimize State reads in Element.computeValue

This CL ensures that we only read the current transition progress in
Element.computeValue so that we don't unnecessarily rerun layout/drawing
code of all elements during transitions.

Test: atest SceneTransitionLayoutTest
Flag: NA
Bug: 305195729
Change-Id: Id1a646caa6be16e5f876987d015af15bf2ae5c4e
2 files changed