winemac: When ClipCursor() is called redundantly, don't warp the cursor or discard mouse move events.

Fixes a problem in some games which repeatedly (re)establish the same cursor
clipping rect, making it exceedingly difficult to move the camera with the
mouse.

In particular, keep the title bar from moving behind the menu bar or Dock (when
it's on the bottom).

user32: In WINPOS_SysCommandSizeMove(), fix constraining a point to a rect's right and bottom edges.

Ddraw and d3d9 already take care of this.

This prevents dragging a window's title bar behind a menu bar across the top
of a screen, for example.

If the target rect is outside a monitor rect but is between its extremes in
one dimension, that dimension should contribute 0 to the distance, rather than
some arbitrary amount.