Dream overlay touch management.

This changelist introduces the DreamOverlayTouchMonitor, a component for observing touches and gestures over the dream overlay and reporting them to a set of consumers. DreamOverlayTouchMonitor is responsible for enabling/disabling touch listening based on the dream overlay service state. It enables listening entities to isolate touches to just their listeners when appropriate and handles resetting listening state across touches.

Bug: 211506329
Test: atest DreamOverlayTouchMonitorTest
Change-Id: I44bcba982dd3a73ebef8cfa52e9ad65216316c08