MDL-71642 qbank_comment: Add question comment plugin to core

This implementation will introduce a qbank plugin
"comment" which will allow users with the capability
to comment in a question. It also implements a
callback for the question preview page to view
and add comments from the preview page. Comment
plugin is implemented using the existing comments
API from the core.

Co-Authored-By: Guillermo Gomez Arias <[email protected]>
Co-Authored-By: Safat Shahin <[email protected]>
Co-Authored-By: Matt Porritt <[email protected]>

lib/classes/plugin_manager.php

@@ -1944,6 +1944,7 @@ class core_plugin_manager {
             ),
 
             'qbank' => [
+                'comment',
                 'deletequestion',
                 'editquestion',
                 'exporttoxml',