Add ScriptLanguage::supports_builtin_mode and improve ScriptCreateDialog

- Make ScriptCreateDialog disable the built-in script checked button if the language does not support it.
- ScriptLanguage's get_template and make_template now receive the script path as class name if the the script language does not have named classes.

modules/gdscript/gd_editor.cpp

@@ -127,6 +127,11 @@ bool GDScriptLanguage::has_named_classes() const {
 	return false;
 }
 
+bool GDScriptLanguage::supports_builtin_mode() const {
+
+	return true;
+}
+
 int GDScriptLanguage::find_function(const String &p_function, const String &p_code) const {
 
 	GDTokenizerText tokenizer;