[VRR] Clear frame rate and category after 250ms idle

Fixes: 338586840

An idle app won't change its category or frame rate while idle.
Howver, that app will still vote with SurfaceFlinger if it is
on screen, even if ocluded.

This CL adds a timeout of 250ms for detecting idle time. If
the time has passed without drawing, the category and frame
rate will reset.

Test: new test, manual testing
Change-Id: Ifc6d81ee8ed97dad7dc9ed5d9a856149a40d8584