feat: Semantic font weights for interactive elements

[kra-mo]

All general text should now be weight 400, interactive controls 500, and headings 600. Also added variables, as suggested by @ShGKme.

Depends on nextcloud/server#59899

☑️ Resolves

• Fix Use font-weight 500 for interactive controls #8083

🖼️ Screenshots

🏚️ Before	🏡 After

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 2️⃣ Backport to stable8 for maintained Vue 2 version or not applicable

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.55%. Comparing base (0aadabf) to head (26567e9).
⚠️ Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8469      +/-   ##
==========================================
+ Coverage   54.47%   54.55%   +0.07%     
==========================================
  Files         105      106       +1     
  Lines        3411     3439      +28     
  Branches      996     1003       +7     
==========================================
+ Hits         1858     1876      +18     
- Misses       1313     1322       +9     
- Partials      240      241       +1     

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[ShGKme]

In addition to the library, we have some global styles for interactive elements, for example:
https://github.com/nextcloud/server/blob/stable33/core/css/inputs.scss

And (barely used) global utils like this:
https://github.com/nextcloud/server/blob/stable33/core/css/global.scss#L75-L77

[susnux]

keep old behavior

[kra-mo]

Ok, I also kept the old values in what were previously removals. It should always use the previous values when variables are not available now, thanks for the help @susnux @ShGKme

[jancborchardt]

Very nice improvement, 👍 design-wise! :)

[ShGKme]

Some fallback values are missing.
Because the variable is not available in older versions, it is better to always have a fallback, even if it is the same value.

[ShGKme]

/backport to stable8