Add methods to query animation state

Testing utilities want the ability to know whether things in the UI
are in flux and they need to wait before testing on-screen values.
These changes (a subset of what's needed, but will have to do for
a start) allow querying of ActivityTransitions and ProgressBar, two
common/difficult pieces in the puzzle.

Test: CTS tests at ag/1835467
Bug: 30978257 Provide view transition Api to prevent flaky tests

Change-Id: If63b3d0dde2178d826ac1dbfad0fc50e5ed9a780