GDK W32: Improve AeroSnap - don't resize windows that fit

GDK W32: Improve AeroSnap - don't resize windows that fit

This is what AeroSnap does. If a window is being unsnapped on
a new monitor, check if the work area is large enough for the
window to fit in its normal size. If the window fits, just
reposition it so that the ratio of
left-window-edge-to-screen-edge / right-window-edge-to-screen-edge
remains the same, without scaling the window.

https://bugzilla.gnome.org/show_bug.cgi?id=763013