fix(a11y): Copy menu entries should be implemented as buttons

[susnux]

• Resolves: [BITV] 9.4.1.2/7.5 - Table / "Copy" menu in the "Message" column - The elements of the menu were incorrectly implemented as links without an href attribute. #883

The copy menu entries should be implemented using buttons instead of links without href set. No visual changes.

[susnux]

/compile amend

[susnux]

/backport to stable27

[icewind1991]

/compile amend

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# 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-stable27

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