gobject: Use construct and construct-only properties
gobject: Use construct and construct-only properties

Right now, we're checking twice for G_PARAM_CONSTRUCT_ONLY, but what we
really want is to check for both G_PARAM_CONSTRUCT and
G_PARAM_CONSTRUCT_ONLY properties when creating a new instance from a
JSON definition.

ebassi/json-glib,Distrotech/json-glib,GNOME/json-glib,oerdnj/json-glib,frida/json-glib,brauliobo/json-glib,Distrotech/json-glib,ebassi/json-glib,brauliobo/json-glib,frida/json-glib,oerdnj/json-glib,robtaylor/json-glib-gvariant,GNOME/json-glib,Distrotech/json-glib,ebassi/json-glib,brauliobo/json-glib,robtaylor/json-glib-gvariant,oerdnj/json-glib,oerdnj/json-glib