Drop vue-clipboard2 in favour of native Clipboard API to fix copy to clipboard

[Pytal]

• Fix [Bug]: Share link in document sidebar not working (when in document edit mode) #36432
• fix [Bug]: Regression: NC 25: Copying internal links from sidebar while document is opened does not work #35922

Summary

Drop https://github.com/Inndy/vue-clipboard2 in favour of the native Clipboard API to copy to clipboard

According to the compatibility table https://developer.mozilla.org/en-US/docs/Web/API/Clipboard/writeText#browser_compatibility only mobile Safari >= 13.4 is compatible, so versions 12.2-12.5 which is targetted by our browserslist https://browserslist.dev/?q=PjAuMjUlLCBub3QgaWUgMTEsIG5vdCBvcF9taW5pIGFsbCwgbm90IGRlYWQsIEZpcmVmb3ggRVNS may not be supported

Before	After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[Pytal]

/backport to stable25

[nimishavijay]

Looks great now 🎉

[szaimen]

CI failure unrelated

[backportbot-nextcloud]

The backport to stable25 failed. Please do this backport manually.

Details

# Switch to the target branch and update it
git checkout stable25
git pull origin/stable25

# Create the new backport branch
git checkout -b fix/foo-stable25

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable25

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

#36507