docs: Add 0.12 symbols index to the API reference
docs: Add 0.12 symbols index to the API reference

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