Add API to query whether animators are enabled

Animators can be scaled to have zero duration globally in any device.
This can happen either via Developer Options (an uncommon path) or
Battery Saver mode (much more common for real users).
In general, this works fine; it just causes app animations to be jump-cuts
instead (which is the desired effect, either to make transitions faster
(Developer Options setting) or to optimize battery usage by rendering
fewer frames (Battery Saver mode).

But sometimes, choreographed animations can have undesired artifacts. For
example, an animation that calls an end listener to restart itself
will end up doing this almost constantly due to this effect. Other artifacts
can also occur, such as intermediate results in a complex choreography of
multiple animations can show several intermediate results in a way that is
confusing to the user.

For these cases, there is nothing that the platform can do to automatically
determine how to best handle the result. Instead, we surface this new
API to help developers discover this behavior and compensate accordingly.

Bug: 31052471 Animation playback is abnormally fast during Battery saver mode
Test: unit tests, CTS test upcoming

Change-Id: Id7ef1a9652ac5c6cdaca0c126756e82582d49b1c