wayland: Do not map toplevel utility as popup

wayland: Do not map toplevel utility as popup

Applications can specify the type hint as utility even on toplevel
windows.

When that toplevel is also marked as a transient for another window,
GDK Wayland backend would translate that as an xdg_popup which is not
appropriate.

While utility temp windows should remain mapped as subsurfaces (such as
the ones used by treeviews), regular windows should not translate as
neither a subsurface nor an xdg_popup.

https://bugzilla.gnome.org/show_bug.cgi?id=781945