window: Tile and resize considering the tile match

After the introduction of the possibility to resize tiled windows,
it is a sensible decision to make windows aware of their tiling
match. A tiling match is another window that is tiled in such a
way that is the complement of the current window.

The newly introduced behavior attepts to make tiling as smooth as
possible, with the following rules:

 * Windows now compute their tile match when tiling and, if there's
   a match, they automatically complement the sibling's width.
 * Resizing a window with a sibling automatically resizes the sibling
   too to be the complement of the window's width.
 * It is not possible to resize below windows' minimum widths.

https://bugzilla.gnome.org/show_bug.cgi?id=645153