Highlight control flow keywords with a different color

This makes them easier to distinguish from other keywords.

modules/visual_script/visual_script.cpp

@@ -2336,6 +2336,10 @@ void VisualScriptLanguage::finish() {
 void VisualScriptLanguage::get_reserved_words(List<String> *p_words) const {
 }
 
+bool VisualScriptLanguage::is_control_flow_keyword(String p_keyword) const {
+	return false;
+}
+
 void VisualScriptLanguage::get_comment_delimiters(List<String> *p_delimiters) const {
 }