Make animated values normal State objects

Before this CL, the State returned by animate(Scene|Element)ValueAsState
was a derivedStateOf {}. This actually did not really make sense, given
that consumers will read the animated value (we are not deriving any
discrete value from the animated one), and also these animated values
are usually read only once so there were probably no benefits of using
derivedStateOf {} at all.

Bug: 317026105
Test: AnimatedSharedAsStateTest
Flag: N/A
Change-Id: If5f6d77346691ac9a1356a0588d5677ff7319228