Call pilfer pointers when second pointer goes down during D&D

We added new functionality to pilferPointers API in ag/18234604.
Using it we can extend the functionality of drag and drop to
allow user to interact with the UI while using 1 pointer/finger
to drag. Pilfering pointers allows gesture monitors to restart
gesture detection with new pointers that down.
Avoid pilfering right after transferTouch on D&D to prevent
security bug: Apps can misuse startDragAndDrop() API to keep
pilfering pointers for gesture monitors and user can get stuck
in an app. Instead we will pilfer when a second pointer goes down
indicating user want to interact while using D&D.

DD: go/global_drag_and_drop

Bug: 220109830

Test: atest inputflinger_tests
Change-Id: I956f040ff307021bb2f74a06228c6addb90e2168