The user is prevented from moving or resizing a maximized window.  The zoom
button is still present and enabled for a maximized window but requests that
it be restored rather than simply resizing it, which is what it does for
normal windows.

If a window is not resizable (lacks WS_THICKFRAME) but has a maximize box
(WS_MAXIMIZEBOX), then the zoom button requests that it be maximized rather
than resizing it.

winemac: Allow programmatic changes of the window frame even if a window is disabled (prevented from resizing).

This won't be enforced if AllowImmovableWindows=n is set in the registry.

This also changes to posting rather than sending WM_SYSCOMMAND/SC_MINIMIZE.