HackStudio: Always re-match curlies/parens after a re-highlight

While you are typing in HackStudio, we re-lex the C++ as you type,
so this means we also need to keep re-checking for matching curlies and
parentheses at the cursor.

Fixes #769 (although it's not optional, because it's too cool. :^)

DevTools/HackStudio/main.cpp

@@ -488,6 +488,7 @@ static void rehighlight()
         spans.append(span);
     }
     current_editor().document().set_spans(spans);
+    static_cast<Editor&>(current_editor()).notify_did_rehighlight();
     current_editor().update();
 }