wbemprox: Rewrite IWbemServices::ExecMethod with low-level functions so we can reuse the object instance.

We generally prevent Cocoa from making our windows key (focused) so that
Wine can be in control.  However, after unminimizing, Wine believes the
window is already focused but Cocoa doesn't, so key presses just cause beeps.

This improves the animation of the window unminimizing from the Dock in some
cases.  The window would often be blank or, for shaped windows, invisible
during that animation.

Minimizing invisible windows causes weird phantoms to appear in
Exposé, the Window menu, and the Dock.