Make AccessibilityGestureEvent.gestureIdToString public.

This allows for better error reporting in tests and services.
Bug: 159651900
Test: atest GestureManifoldTest TouchExplorerTest AccessibilityGestureDetectorTest FrameworksServicesTests:TouchExplorerTest

Change-Id: Ic65ff7100ade77bbf26d538a033e9e000e6b9bcc
2 files changed