PriorityNestedScrollConnection: make onStop suspendable and add onCancel

The onStop lambda is now a suspend function. This allows for performing
long-running operations, such as animations, within the onStop callback.

The onCancel lambda has been added, this lambda will be invoked when the
nested scrolling operation is canceled, for example, if the user cannot
scroll anymore.

Test: atest PriorityNestedScrollConnectionTest
Bug: 370949877
Flag: com.android.systemui.scene_container
Change-Id: I4cc652fe4f6baac800e1484e7bddfbf5510de2b1