Hide the A11yMenu UI before performing actions instead of after.

This should help prevent the A11yMenu UI from accidentally appearing in
screenshots on some devices.

Test: Use all shortcut actions, observe no change in behavior.
Test: Repeatedly use screenshot action, observe menu UI is never
      included in a screenshot.
Fix: 292020123
Change-Id: I262f3235962ae98e8772e8d60686508ef114c8b6