Add a thin declarative API for defining script methods/properties

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.

test/script/CMakeLists.txt

@@ -7,6 +7,8 @@ include(dusktest)
 
 dusktest(test_modulerequire.c)
 
+dusktest(test_scriptdef.c)
+
 dusktest(test_overworldscene.c)
 target_compile_definitions(test_overworldscene PRIVATE
   DUSK_ASSETS_DIR="${DUSK_ASSETS_DIR}"