Change drag to edge to requestSplit when not in freeform.

When in fullscreen or split, dragging a task using the handle would move
the task to freeform in split snap bounds. This change makes it so the
task instead requests splitscreen windowing mode.

Test: Manual
Test: atest DragToDesktopTransitionHandlerTest
Bug: 336310725
Change-Id: Idf232146e625a193960a8d9497f116eb3e4ac0e4