Add TransitionBuilder.reversed()

This CL adds TransitionBuilder.reversed() to be able to explicitly
reverse some transformations. This can be used to partially share the
transition definition of Foo => Bar when defining Bar => Foo. This will
be used to make it possible to disable shared element animation in the
Shade => Lockscreen transition while keeping it enabled in the
Lockscreen => Shade transition.

Bug: 300867076
Test: atest TransitionDslTest
Change-Id: Iaddfdf5eab0d1990d54ac6081948ab9b4c763f66