Clean up placement code

Sometimes the XdgToplevelWindow needs to run the placement code. But with the current architecture, it's difficult to achieve because of move() and moveResize() calls in the Placement.

As the first step, the patch series in this MR ensures that every placeXyz() function calls move() or moveResize() only once. It also drops all usages of Window::frameGeometry() for the to be placed window because it can be considered as invalid and that's the reason why we run the placement code: to get a suitable position for the window.

The next steps would be to hoist move() and moveResize() out of the Placement and let the Window take care of it.