LibJS: Implement constructor/non-constructor function calls

This adds Function::construct() for constructor function calls via `new`
keyword. NativeFunction doesn't have constructor behaviour by default,
ScriptFunction simply calls call() in construct()

Libraries/LibJS/Runtime/NativeFunction.cpp

@@ -44,4 +44,9 @@ Value NativeFunction::call(Interpreter& interpreter)
     return m_native_function(interpreter);
 }
 
+Value NativeFunction::construct(Interpreter&)
+{
+    return {};
+}
+
 }