Do not send updates for disabled displays.

If a display is disabled, do not share it outside of
DisplayManagerService.

This will help by not creating any unnecessary updates for displays that
are disabled, and also not informing Applications of displays that they
are unable to use.

Also fixing a concurrency issue with DMS.handleLogicalDisplaySwapped
which became apparent with this CL. Deferring the runnable with a
Handler.post() caused the display-state-OFF update to happen after a newer
change to turn the display ON.  This caused the device to startup into a
black screen. Removed the unnecessary call (since the displays are now
made to both go into the "transition" state) to update the state and
removed a lot of the redundant code with handleLogicalDisplayChange()
which was called at the end of the method anyway.

Bug: 221071695
Test: atest com.server.android.display
Test: Manually verify display layouts still successfully change, and
      also confirm logs no longer hand excessive add/remove
      display notifications.
Change-Id: I003fd91567630a447cf030b6fb83e5cb1041bcb5