feat(link): Toggle link on selection with Mod-K shortcut

[mejo-]

Acts only upon selection as inserting a link with empty title creates an invisible link, resulting in bad user experience in the WYSIWYG editor.

Fixes: #7152

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits

[mejo-]

/backport to stable31

[codecov]

Codecov Report

Attention: Patch coverage is 38.70968% with 19 lines in your changes missing coverage. Please review.

Project coverage is 52.51%. Comparing base (bf3594e) to head (f16579a).
Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/Link/LinkBubbleView.vue	0.00%	12 Missing ⚠️
src/marks/Link.js	46.15%	7 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #7188 +/- ##
==========================================
+ Coverage 52.41% 52.51% +0.10% 
==========================================
Files 479 479 Lines 41508 41545 +37 Branches 1024 1024 ==========================================
+ Hits 21757 21819 +62 + Misses 19649 19624 -25 
Partials 102 102 

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[luka-nextcloud]

I've tested and it works well 👍