Missing RecordRTC icons from Atto editor

Moodle 3.5 has introduced the ability to record audio/video directly into the Atto editor via the RecordRTC icons/buttons.

However, as a teacher, when entering feedback comments in the Assignment activity, there are no RecordRTC icons in the Atto editor. 

1. Add an assignment activity to a course, configure with Feedback comments enabled
2. Log in as a student and submit an assignment
3. Log in as a teacher
4. Go to the Assignment activity and click on [Grade] to grade the student

As a consequence, it is not possible to record video/audio directly into the Atto editor for a Teacher giving Feedback comments in an Assignment.

https://tracker.moodle.org/browse/MDL-60848  states that this functionality should "crucially, add the capability for this to be used in the HTML feedback part of the assignment and gradebook so that multi-media feedback can be given"