Steps to reproduce
===============

1. Create an Activity with HTML entities in the name, such as:

A "Test" Activity & Perhaps More & Then Some

2. Enable course's Completion Tracking and an activity's manual Activity Completion.

3. Hover over the activity's completion checkbox to see the title text with HTML entities.

Actual result
==========

For example, when hovering over its checkbox, an incomplete activity having the name from above will show with HTML entities. Note the single "&" is converted to &

Not complete: A "Test" Activity & Perhaps More & Then Some. Select to mark as complete.

If you then toggle the checkbox to Incomplete, it will still show with HTML entities as:

Completed: A "Test" Activity & Perhaps More & Then Some. Select to mark as not complete."

But notice that only the explicitly specified & stays encoded, while the last ampersand now displays correctly as a single "&", as it was originally in the activity name.

Expected result
============

All strings with the activity name should always show with decoded HTML entities. In the example above, it should show as it does on the activity page itself:

 A "Test" Activity & Perhaps More & Then Some

Other points
==========

• The text for the initial page load is handled by course_section_cm_completion() in /course/renderer.php. I imagine the fix might be to just add $imgalt = html_entity_decode($imgalt).
• However, subsequent clicks to toggle the completion checkbox on and off will go through /course/completion.js. The JS code will also need to decode the HTML entities, since it is pulling the activity name (module name) from the hidden <input name="modulename"> element.
• Similar issue: https://tracker.moodle.org/browse/MDL-59797