Dispose of TaskResizeInputEventReceiver when needed

Fixes a resource leak caused by the DragResizeInputListener ctor
creating an InputEventReceiver and never disposing of it when the
listener is closed.

Bug: 269431952
Test: manual - enter desktop mode, resize freeform task, make it
full screen and close it. Wait a couple of minutes and verify no
StrictMode violation are reported in the logcat

Change-Id: Ia1ee47d1ba55665fb5dc6116893435e189a3be26