MultiPointerDraggable should not lose pointerInput events

In aosp/2156636 a lint was added: launching multiple
awaitPointerEventScope blocks might cause some of the input events to be
dropped leading to unexpected behaviors.

Now, there are two suspending pointer input modifiers. The first keeps
track of the number of fingers and the initial position, while the
second takes care the multidrag behavior.

Test: Manually tested.
Bug: 336710600
Flag: com.android.systemui.scene_container
Change-Id: I6403cd2f2ab750e502e4c2bff90116cef955b4ed