Rename WindowDecorModelView to reflect purposes

Changed method names in WindowDecorModel Interface to better reflect
their purposes and made onTaskChanging (Previously
setupWindowDecorationForTransition) to handle captionCreation if needed.

Test: Manual Testing and created CaptionWindowDecorViewModelTests
Bug: 257288823
Change-Id: I43672fa37accba97b4ea330e01082d00137a4b01