Compose gesture integrated fully into Launcher

- Support dismissing Compose via the reverse gesture from the appear
gesture
- Use Tony Wickham's ag/10204761 with some glue code to enable the
app below Compose panning in the same direction as the gesture as
Compose peeks in
- Add feature flag to use Compose hosted in a window (permits underlying
app panning)
- Use InterpolatingVelocityTracker to fix OtherActivityInputConsumer
processing swipes in the wrong direction ~20% of the time due to a bug
in VelocityTracker (see go/quirky-bubbles)

Change-Id: I65aa07ac112db8bd89cec9acfa0ce2b6ebacd43f