scriptvalue.h/.c holds the scriptvalue_t tagged-union type and its
JS<->C decode/encode helpers; scriptdef.h/.c holds the declarative
scriptfuncdef_t/scriptpropdef_t definitions, the binding registry,
and the JerryScript trampolines. Lets a module declare its JS-facing
methods/properties/globals as typed data instead of hand-writing
argument-checking boilerplate per method. Framework only for now --
no existing module has been migrated onto it yet.
