Update the tests build to be a testing unit
Update the tests build to be a testing unit

Instead of having stand alone tests, use the GTest framework and start
coalescing multiple test cases into one.

The tests directory will be used for JsonParser, JsonGenerator and
the JSON-GObject integration API, by reusing the previous test cases
and remolding them into a more interesting test framework.

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