[wm]: ensure task positioner controller is always cleaned up

If freeform windowing app is killed while moving, future touch action does not work.
TaskPositioner state is not reset properly. So InputChannel for positioning a task
consumes all touch event.

Finish task positioning when calling session process is killed.

Test: manual - Kill freefrom windowing task process while dragging it
Test: atest WmTests:TaskPositionerTests
Bug: 129492888
Change-Id: I7eb392d6d87a118dd85e7d752eaabfe600920794
(cherry picked from commit 70fe14b649461d9632f24db844b6054879df60b9)