Cleanup mOpenGesturesInProgress to use a simple boolean.

This SparseArray is only ever used to make decisions for events
with source == EVENT_SOURCE, so this change simplifies that array
to use a single boolean instead of an array of booleans.

Bug: 384451671
Test: existing tests in presubmit
Flag: EXEMPT no-op refactoring
Change-Id: Ie20fc3a43d4a15f433953ead94bdc31c578d0eb8