Use retryAfter() and handleRetriesFor() from mathjax so they are easier to override

[dpvc]

This PR moves the references to retryAfter() and handleRetriesFor() to the version in the mathjax variable rather than from the Retries.ts module directly. This makes it easier to override them. I have an example of making MathJax load tex extensions synchronously that would be helped by this, as that means there would be fewer methods that need to be overridden. Together with the synchronous loading of dynamic font data and of entity definitions, this would allow MathJax to be run synchronously in node applications, where synchronous file loading can be achieved.

Note that asyncLoad uses mathjax.asyncLoad internally, so we don't have to use mathjax for that.

[codecov]

Codecov Report

❌ Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.98%. Comparing base (6c2be35) to head (f9610c3).
⚠️ Report is 21 commits behind head on develop.

Files with missing lines	Patch %	Lines
ts/core/MathDocument.ts	0.00%	3 Missing ⚠️
ts/output/common/FontData.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1547      +/-   ##
===========================================
+ Coverage    86.92%   86.98%   +0.05%     
===========================================
  Files          390      390              
  Lines        87853    87764      -89     
  Branches      4984     4983       -1     
===========================================
- Hits         76370    76343      -27     
+ Misses       11464    11402      -62     
  Partials        19       19              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[zorkow]

I have two concerns about the new async loading. Please have a look.

[zorkow]

This now returns a promise regardless of if it fails or not. So the try...catch does not really have an effect on this. But that means that dynamic.failed is never set. That would mean the file is set to loaded
even if the promise failed.

[zorkow]

Similarly, should the promise failure here not be handled explicitly?

[dpvc]

I have put back the mathjax.asyncLoad() calls to what they used to be. Do you need to re-review?

[zorkow]

I have put back the mathjax.asyncLoad() calls to what they used to be. Do you need to re-review?

No, that looks good now.