fix min/max constraints when restoring from maximized and fullscreen mode

Mutter inconsistently constrains fullscreen windows but not maximised windows. Fixed-sized window will not get maximised when xdg_toplevel.set_maxmized is requested, but xdg_toplevel.set_fullscreen will make the shell behave as if a window is fullscreen although its toplevel surface will still be constrained by the min/max size. This is inconsistent behaviour and also an inconsistent visual representation.

Since the client is in charge of the toplevel behaviour anyway, this MR simply changes this so that all windows can be maxmised and fullscreened, regardless of their min/max limits. Additionally, this MR fixes an issue when restoring a fullscreen window to its previous floating state.

Fixes: #1735