Support launching an intent based drag into split

- Extend support for launching intent drags into splitscreen in
  addition to crafted app drags sourced from SystemUI
- Unlike app drag drags which are consumed for the whole display,
  intent drags only invoke split from the side edges of the screen,
  so we need to manipulate the touchable region of the shell drop
  target based on the drag data in the current drag session

This reverts commit 41dc803ab1e79305304b3ad67e0ef8e35c33332e.
Bug: 320797628
Test: atest WMShellUnitTests
Test: https://recall.googleplex.com/projects/e3f080d7-2818-43f0-a087-405000b8fdf5/sessions/e88a0470-6850-43a0-abfa-3366b7c7c6a4

Change-Id: I3c0946ae06ae03c21c189c1df1dba3d47db77eb9