Sync granularity of gestures with vsync

Gesture dispatch should match the refresh rate of the Display, in order
to create smooth animations. The previous behavior was to split gestures
up into 100ms steps. Retain that behavior for AccessibilityService
instances that are targeting pre-R. For R, split gestures up into enough
steps to closely track refresh rate.

Test: manual
Bug: 150190594
Change-Id: I80b24227f86916945abf7ff8bfb60a91fc12f50e