Cache flag value for AnmationUtils

As suggest in
https://buganizer.corp.google.com/issues/301713352#comment17, the usage
of Trunk Stable flag can slow down Choreographer. Thus, this CL is
create to cache the flag value locally

I added a new flag as suggested by flag team - "change the `is_fixed_read_only` type on an existing flag currently is not supported unfortunately. so you may need to create a new flag"

Fix: b/301713352
Test: atest AnimationUtilsTest
Change-Id: I1cb418161f7736e66f75419ab48d4a8fde8b4259