Consume pending display config change with multiple remote callbacks

For example:
Callback1 { sendNewConfiguration }
Callback2 { applySomething }

If Callback1 completes first, its sendNewConfiguration won't take
effect because isWaitingForRemoteDisplayChange is true by the
pending Callback2. And then when Callback2 completes, it only
perform its own operations.

So this change provides a callback from display to make sure its
pending config change can be handled when all remote callbacks
are done.

Fix: 305655839
Test: atest DisplayContentTests#testRemoteDisplayChange
Merged-In: I64897baeaa0b5d81c904d75f2b1e17c0eefec3bf
Change-Id: I64897baeaa0b5d81c904d75f2b1e17c0eefec3bf