x11: Handle late sync request

X11Client implicitly relied on the finishInteractiveMoveResize() function
to call moveResize() to synchronize the move resize geometry with the
server geometry. However, after removing that moveResize(), X11Client
got slightly broken.

A resize sync request may arrive shortly after finishing resize. In
order to properly handle it, this change makes X11Client handle late
sync requests.

It also makes handling interactive resize on x11 similar to how it's
done on wayland.

The main problem with not letting X11Client finish interactive resize
is that the Toplevel::bufferGeometry() may end up with an outdated value
and SurfacePixmapX11 will fail to create due to a mismatch between
Toplevel::bufferGeometry() and the server side geometry of the frame
window.