Store a copy of the motion event

Motion events that are recycled and then re-used can result in bad
behaviour (i.e crashes) if they are not initialised correctly - see
b/273963331. The guidance is to reinitialise these events before use to
ensure they are initialised correctly.

Flag: EXEMPT bug fix
Fixes: 423744011
Test: atest WMShellUnitTests:DragDetectorTest,
      atest WMShellUnitTests:DragResizeInputListenerTest
Change-Id: I731af1ae311dfa6f8697655de19bd4151bc78241