multiPointerDraggable set an order for PointerEventScopes

The order is important here: we want to make sure that the previous
PointerEventScope is initialized first. This ensures that the following
PointerEventScope doesn't receive more events than the first one.

Test: A lot of manual testing (Hard to reproduce it, seems a race condition)
Bug: 352522308
Flag: com.android.systemui.scene_container
Change-Id: Iba816edd0cd3a62c3acc8ee3ff5af746b0293905