Implement `JSON[ @@toStringTag ]` (#1224)

boa/src/builtins/json/mod.rs

@@ -41,7 +41,12 @@ impl BuiltIn for Json {
     fn init(context: &mut Context) -> (&'static str, Value, Attribute) {
         let _timer = BoaProfiler::global().start_event(Self::NAME, "init");
 
+        let to_string_tag = context.well_known_symbols().to_string_tag_symbol();
+
+        let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE;
+
         let json_object = ObjectInitializer::new(context)
+            .property(to_string_tag, "JSON", attribute)
             .function(Self::parse, "parse", 2)
             .function(Self::stringify, "stringify", 3)
             .build();