build: Restructure scalar typedefs in graphene-config.h
build: Restructure scalar typedefs in graphene-config.h

We use the `/*< private >*/` trigraph, but the parsers have had troubles
in the past if the definition of a structured type sits on just one
line.

criptych/graphene,criptych/graphene,ebassi/graphene,ebassi/graphene,criptych/graphene,criptych/graphene