feat(NcRichText): add 'Copy to clipboard' button for code blocks

[Antreesy]

☑️ Resolves

• Attempt to upstream clipboard functionality from Talk
• Logic based on NcFormBoxCopyButton
• Works with plain text and highlighted syntax

🖼️ Screenshots

🏡 After

🚧 Tasks

• Move useCopy to composables?
• Extract CopyButton as standalone component?
• Need a prop to enable/disable?

🏁 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 52.11%. Comparing base (6523151) to head (9cf7ad7).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7841      +/-   ##
==========================================
- Coverage   52.12%   52.11%   -0.02%     
==========================================
  Files          98      100       +2     
  Lines        3150     3170      +20     
  Branches      869      873       +4     
==========================================
+ Hits         1642     1652      +10     
- Misses       1262     1271       +9     
- Partials      246      247       +1     

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[Antreesy]

/backport to stable8