Improved `dumpsys device_config` so it calls the mainline implementation.

That will allow it to include more information, like the property
change listeners. Example:

$ adb shell dumpsys device_config | grep listeners | head -3
245 listeners for 185 namespaces:
   accessibility: 2 listeners
   activity_manager: 5 listeners

Bug: 364399200
Test: see above
Flag: android.provider.flags.dump_improvements

Change-Id: Ifab219bccededb07de558dced9d6203efe568042