Do not send updates for disabled displays.

If a display is disabled, do no share it outside of
LogicalDisplayMapper.

This will help by not creating unnecessary updates for displays that
are disabled.

Bug: 197515205
Bug: 221071695
Test: atest com.server.android.display
Test: Manually verify display layouts still successfully change, and
      also that confirm logs no longer have excessive add/remove
      display notifications.
Change-Id: Ie5954935bb1afc612935e52d421b0e103d8d0854