Populate AccessibilityEvent.getAction when preforming an action

This change populates the action in AccessibilityEevnt when this event
is dispatched while performing an accessibility action.

Note that there is no guarantee that action is always populated for
any action because developers can handle actions in their delegate.

Bug: 151398335
Test: none. (manually confirm that the value is populated)
Change-Id: I3fc46ba9df239c665ad5d804d2b81b366f5dd3de