wayland: unmaximised window dimensions are not restored from tiled mode

Mutter does not restore the window dimension when a Wayland application is untiled, i.e. a window keeps its tiled dimension after it is restored from a left/tight tiled state.

1. start weston-terminal or Qt's analogclock example (with -platform wayland), the applications starts with its original initial unmaximised/untiled window dimension U
2. tile left or right via Super + Left/Right or by dragging to the left/right screen border, the application will be tiled with dimension T that will be full height and half width of the maximised dimension
3. un-tile the application by Super + Down or by dragging it away from the border
4. the applications should restore it's original window dimension U but keeps the tiled dimension T

Related to this, GTK applications do attempt to restore their original window dimension but restore the window with a smaller size than U (#140 (closed)).