Move user event loop callback to it's own API

[Meakk]

Describe your changes

Needed for #3051

At the moment, when using triggerEventLoop() manually there's no way to specify the user callback.
It would also be odd to pass the user callback each time we want to trigger the event loop manually, so let's move it to its own API so the user can set it once.

Also added a documentation for migration to 4.0.

Issue ticket number and link if any

Checklist for finalizing the PR

• I have performed a self-review of my code
• I have added tests for new features and bugfixes
• I have added documentation for new features
• If it is a modifying the libf3d API, I have updated bindings
• If it is a modifying the .github/workflows/versions.json, I have updated docker_timestamp

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• ...

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[github-actions]

You are modifying libf3d public API! ⚠️Please update bindings accordingly⚠️!
You can find them in their respective directories: c, python, java, webassembly.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.06%. Comparing base (12a0ede) to head (141a18a).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3115      +/-   ##
==========================================
- Coverage   97.12%   97.06%   -0.06%     
==========================================
  Files         208      208              
  Lines       16705    16717      +12     
==========================================
+ Hits        16225    16227       +2     
- Misses        480      490      +10     

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[mwestphal]

Looks good, nothing in javascript bindings I suppose ?

[mwestphal]

one small last change

[Meakk]

Windows CI broken, not related, merging