Formatting in the RTE should be rendered at the back end

Found while investigating CONF-20124 - when selecting a formatting option like "Code" the result is different after round-tripping.

To reproduce:

1. In the RTE enter the text <script>alert("Hello cruel world")</script>
2. Select the Code format - the text will be wrapped in a box
3. Go to wiki-markup - the text will be wrapped in {code} tags
4. Go back to the RTE - the text will now have syntax highlighting on the string "Hello cruel world"
   The syntax highlighting should have been applied immediately, which can only happen if the code macro block including the text is rendered by the server.