Improve collapse behavior

[nwalters512]

This is being done ahead of Bootstrap 5. In v5, they changed how data-toggle="collapse" is handled. Now, they handle click events for that in the capturing phase instead of the bubbling phase (see twbs/bootstrap#36063). This means that we no longer have the option of using stopPropagation() to ensure that clicks on nested buttons don't toggle the open/closed state. I opened twbs/bootstrap#40574 to change Bootstrap to handle these events in the bubbling phase, but that's unlikely to be reviewed or released soon.

Now, collapse toggling is controlled only by an explicit button. The main user-facing change is that clicking on question submission/feedback panel headers will no longer toggle the open/closed state of the panel. IMO this is strictly (if indeed slightly) worse, but 🤷

I made some accessibility improvements as I went:

• I added some missing aria-expanded/aria-controls attributes
• I changed pl-external-grader-results to use a button as a toggle instead of a div. This ensures that it can be navigated and operated with a keyboard.

[github-actions]

All images

Image	Platform	Old Size	New Size	Change
prairielearn/executor:6e4881fb5d8e3134bfa8c4a2ef2cf6b533f64c0d	null	1185.44 MB	1185.27 MB	-0.01%
prairielearn/prairielearn:6e4881fb5d8e3134bfa8c4a2ef2cf6b533f64c0d	linux/amd64	1185.43 MB	1185.27 MB	-0.01%

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 71.62%. Comparing base (10db4a2) to head (6e4881f).
Report is 1 commits behind head on master.

Files	Patch %	Lines
...ielearn/src/components/CourseRequestsTable.html.ts	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10467      +/-   ##
==========================================
+ Coverage   71.61%   71.62%   +0.01%     
==========================================
  Files         526      526              
  Lines       82763    82765       +2     
  Branches     6935     6939       +4     
==========================================
+ Hits        59268    59284      +16     
+ Misses      23033    23018      -15     
- Partials      462      463       +1     

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