EditorSettings: Dehardcode major in config file name

It was readded in panic after I mistakenly removed the hardcoded "-3" in #12988,
forgetting that Windows would still use the same path and thus conflict with 2.1
(contrarily to macOS and Linux).

editor/editor_settings.cpp

@@ -789,7 +789,7 @@ void EditorSettings::create() {
 
 		// Validate editor config file
 
-		String config_file_name = "editor_settings-3.tres";
+		String config_file_name = "editor_settings-" + itos(VERSION_MAJOR) + ".tres";
 		config_file_path = config_dir.plus_file(config_file_name);
 		if (!dir->file_exists(config_file_name)) {
 			goto fail;