Remove VARIANT_ARG* macros

* Very old macros from the time Godot was created.
* Limited arguments to 5 (then later changed to 8) in many places.
* They were replaced by C++11 Variadic Templates.
* Renamed methods that take argument pointers to have a "p" suffix. This was used in some places and not in others, so made it standard.
* Also added a dereference check for Variant*. Helped catch a couple of bugs.

modules/visual_script/visual_script_nodes.cpp

@@ -3174,7 +3174,7 @@ public:
 			r_error.error = Callable::CallError::CALL_ERROR_INVALID_METHOD;
 			return 0;
 		}
-		*p_outputs[0] = subcall->call(VisualScriptLanguage::singleton->_subcall, p_inputs, input_args, r_error);
+		*p_outputs[0] = subcall->callp(VisualScriptLanguage::singleton->_subcall, p_inputs, input_args, r_error);
 		return 0;
 	}
 };