Entirely removes BIND_VMETHOD in favor of GDVIRTUAL

* `_gui_input`, `_input`, `_unhandled_input` and `_unhandled_key_input` are now regular C++ virutal functions.
* Everything else converted to GDVIRTUAL
* BIND_VMETHOD is gone, always use the new syntax from now on.

Creating `_gui_input` method and using the binder to register events will no longer work, simply override the virtual function now.

editor/editor_help_search.cpp

@@ -71,7 +71,7 @@ void EditorHelpSearch::_search_box_gui_input(const Ref<InputEvent> &p_event) {
 			case KEY_DOWN:
 			case KEY_PAGEUP:
 			case KEY_PAGEDOWN: {
-				results_tree->call("_gui_input", key);
+				results_tree->gui_input(key);
 				search_box->accept_event();
 			} break;
 			default: