Improve files version listing

[artonge]

In too many cases, the list of version in the DB failed to match the list of version in the FS.

This PR changes the listing approach
from: "return DB listing unless it is empty, if it is empty, then populate DB based on FS and return DB listing"
to: "return a merge of DB and FS listing, while doing the merge, prune DB entries if no counterpart FS entries exist, and create DB entries if it is missing".

This trades a bit of performance, against DB integrity, code simplification, and reliability.

Possible followups:

• Check if groupfolders can be improved as well
• Reduce complexity of file event listener as we do not need to closely manage DB entity anymore.

[artonge]

/backport to stable28

[artonge]

/backport to stable27

[backportbot]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28
# Create the new backport branch
git checkout -b backport/43898/stable28
# Cherry pick the change from the commit sha1 of the change against the default branch# This might cause conflicts, resolve them
git cherry-pick 87057278
# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/43898/stable28

Error: Failed to push branch backport/43898/stable28: fatal: could not read Username for 'https://github.com': No such device or address

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[artonge]

/backport to stable28

[mahibi]

/backport to stable26

[artonge]

/backport to stable26