LibJS: Add JSON.stringify

Author: https://github.com/mattco98
Commit: 39576b2238
Pull-request: https://github.com/SerenityOS/serenity/pull/2545
Reviewed-by: https://github.com/Dexesttp
Reviewed-by: https://github.com/awesomekling

Libraries/LibJS/Runtime/ArrayConstructor.cpp

@@ -81,10 +81,7 @@ Value ArrayConstructor::construct(Interpreter& interpreter)
 Value ArrayConstructor::is_array(Interpreter& interpreter)
 {
     auto value = interpreter.argument(0);
-    if (!value.is_array())
-        return Value(false);
-    // Exclude TypedArray and similar
-    return Value(StringView(value.as_object().class_name()) == "Array");
+    return Value(value.is_array());
 }
 
 Value ArrayConstructor::of(Interpreter& interpreter)