Don’t consider move without actual bounds change as drag

This CL prevents DMWindowDecor from flipping `mIsDragging` for
ACTION_MOVE without actual bounds change.
Otherwise, no one resets the flag when...
 1) ACTION_DOWN on caption button
 2) ACTION_MOVE without actual bounds change on caption button
    Note that ACTION_MOVE can be fired even when there is no position
    change from the previous ACTION_DOWN
 3) ACTION_UP on caption button
 4) onClick on caption button
so the caption button click is ignored.

Bug: 364990718
Test: DesktopModeWindowDecorViewModelTests
Flag: EXEMPT bugfix
Change-Id: Icc15380b26f85c93a724966a7e09472b56f0d259