Split the Syntax Highlighting extension in two extensions

Keep in the current extension only the code which transforms each textarea in XWiki 'edit' mode into CodeMirror instances.
Create a new extension which contains a RequireJS module allowing the user to transform a given textarea into a CodeMirror instance. This extension will be used as a dependency for the first one.

Other extensions that require CodeMirror instances, such as the Web IDE application, could then use the new RequireJS module as a dependency instead of the whole Syntax Highlighting extension.