Add default implementation of `ScriptLanguageExtension::preferred_file_name_casing`.

core/object/script_language_extension.h

@@ -389,7 +389,16 @@ public:
 	EXBIND0RC(bool, can_make_function)
 	EXBIND3R(Error, open_in_external_editor, const Ref<Script> &, int, int)
 	EXBIND0R(bool, overrides_external_editor)
-	EXBIND0RC(ScriptNameCasing, preferred_file_name_casing)
+
+	GDVIRTUAL0RC(ScriptNameCasing, _preferred_file_name_casing);
+
+	virtual ScriptNameCasing preferred_file_name_casing() const override {
+		ScriptNameCasing ret;
+		if (GDVIRTUAL_CALL(_preferred_file_name_casing, ret)) {
+			return ret;
+		}
+		return ScriptNameCasing::SCRIPT_NAME_CASING_SNAKE_CASE;
+	}
 
 	GDVIRTUAL3RC(Dictionary, _complete_code, const String &, const String &, Object *)