LibJS: Rework how native functions are called to improve |this| value

Native functions now only get the Interpreter& as an argument. They can
then extract |this| along with any indexed arguments it wants from it.

This forces functions that want |this| to actually deal with calling
interpreter.this_value().to_object(), and dealing with the possibility
of a non-object |this|.

This is still not great but let's keep massaging it forward.

Libraries/LibJS/Interpreter.cpp

@@ -190,7 +190,7 @@ Value Interpreter::call(Function* function, Value this_value, const Vector<Value
     auto& call_frame = push_call_frame();
     call_frame.this_value = this_value;
     call_frame.arguments = arguments;
-    auto result = function->call(*this, call_frame.arguments);
+    auto result = function->call(*this);
     pop_call_frame();
     return result;
 }