Stop creating multiple JS classes on demand, and instead use the
same JS class and create multiple constructors with different
prototypes, but hand-rolling our own version of JS_InitClass, that
also avoids polluting the global object.
This means that JS_ConstructObject is no longer usable with dynamic
classes, use gjs_construct_object_dynamic or JS_New instead.

https://bugzilla.gnome.org/show_bug.cgi?id=679688