Wait for the MathJax.startup.promise to update the feedback popoer.

The `inserted.bs.popover` event still does not occur late enough for the
MathJax `typesetPromise` to be defined on the page sometimes. I am not
seeing this once the update is deferred a bit more with a `setTimeout`
call.  So wait on the `MathJax.startup.promise` to be fulfilled before
updating.

One way to see the issue is to set the "Assist with the student answer
entry process" option to "MathView".  Then click the "Show Correct
Answers" button in a problem with multiple answers (it can occur with
one answer, but more reliably occurs with multiple answers).  The
popovers are not positioned correctly.

Another way to see the issue is to add `console.log(MathJax.typesetPromise)`
on the line before the change in this pull request (even with MathQuill
enabled).  You will see that most of the time, that is undefined.

Author: drgrice1

htdocs/js/Feedback/feedback.js

@@ -13,7 +13,10 @@
 
 		feedbackBtn.addEventListener('inserted.bs.popover', () => {
 			// Render MathJax previews.
-			if (window.MathJax) MathJax.typesetPromise?.([feedbackPopover.tip]).then(() => feedbackPopover.update());
+			if (window.MathJax)
+				MathJax.startup.promise
+					.then(() => MathJax.typesetPromise([feedbackPopover.tip]))
+					.then(() => feedbackPopover.update());
 
 			// Execute javascript in the answer preview.
 			feedbackPopover.tip?.querySelectorAll('script').forEach((origScript) => {