Deprecate the className prop

[remcohaszing]

Initial checklist

• [x] I read the support docs
• [x] I read the contributing guide
• [x] I agree to follow the code of conduct
• [x] I searched issues and couldn’t find anything (or linked relevant results below)
• [x] If applicable, I’ve added docs and tests

Description of changes

This deprecates the className prop, but does not remove it yet. Users should wrap the <Markdown> component inside a <div> manually instead.

Closes #781

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• [ ] Initial checklist (todo)
• [x] Description of changes

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### Initial checklist

*   [ ] I read the support docs <!-- https://github.com/remarkjs/.github/blob/main/support.md -->
*   [ ] I read the contributing guide <!-- https://github.com/remarkjs/.github/blob/main/contributing.md -->
*   [ ] I agree to follow the code of conduct <!-- https://github.com/remarkjs/.github/blob/main/code-of-conduct.md -->
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### Description of changes

TODO

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Thanks, — bb

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (2245c64) 100.00% compared to head (40143b1) 100.00%. Report is 3 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff            @@
##              main      #799   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines         1354      1337   -17     
  Branches       113       110    -3     
=========================================
- Hits          1354      1337   -17     

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[remcohaszing]

I misinterpreted the meaning of the word deprecated here originally in a late evening.

I interpret deprecated as planned for change or removal with a warning. In this project deprecated means removed with an error, making deprecations semver major.

[wooorm]

Can you drop the changelog entry? I’ll write the changelog/migration manually when the time is there! Otherwise, :+1:

[remcohaszing]

Sure :+1:

It just feeld a bit weird to link a non-existent header from the code.

[wooorm]

Ah that’s why, hmm, then I’d do a <!-- To do: add heading for slug deprecate-classname --> Or these two comments might be enough!

[remcohaszing]

Since this change is breaking, this PR shouldn’t be merged until the next major anyway. I think this PR thread is plenty reminder once this gets merged. :)