If the focus changes between Wine windows, the wineserver logic will
decide to reset the clipping rectangle. However winex11 also needs to
support the case when focus changes to a host window, in virtual desktop
mode, and in this case the foreground window doesn't actually change.

To fix this, in virtual desktop mode, release the cursor on focus out
events, and reapply the cursor clipping rect when the virtual desktop
window is focused again.

We can use the same logic on NotifyGrab events, when the WM grabs the
keyboard, and later reapply the Wine clipping rect when we are notified
about the keyboard ungrab.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=55046