Hide touchable surface from accessibility

Currently the glanceable hub touchable surface registers two actions, a
single tap for showing an unlock prompt, and a long press for showing
the cutomize widgets prompt. Neither of these action is necessary for
accessbility as user can get to them through other accessbility actions.

This change hides these actions from accessibility.

Test: verified the touchable surface no longer shows up when switch
      access is enabled
Test: verified still able to customize widgets through custom actions
Test: verified still able to see unlock prompt through either the first
      full screen action or selecting the lock icon
Fix: 377174999
Flag: com.android.systemui.communal_hub
Change-Id: Ie045582ae33f9697adbf66f04fd82cd191475dc4