Fix federated reshares

[provokateurin]

The following sharing chain didn't work before:

1. User A from instances A creates public share link
2. User B from instance B uses the "Add to your Nextcloud" feature
3. User B from instance B creates a public share link
4. User C from instance C uses the "Add to your Nextcloud" feature

Without these fixes step 4 fails:

server/apps/federatedfilesharing/lib/Controller/MountPublicLinkController.php

Line 124 in dd38de7

$this->federatedShareProvider->create($share);

causes $share->setId($shareId); to be called on a share that already has an id set, which fails because it's not allowed. The share from user A to user B is also removed due to bad error handling after the exception.

I'm afraid the PublicOwnerWrapper is broken as well, because the code doesn't consider that the owner might be a user from a different instance, but I'm not sure if that can be fixed at all without huge changes. Maybe this scenario could be detected and the initiator could be used as a replacement, but that could also have other unintended side effects.

[come-nc]

I agree with @salmart-dev I think. For the rest, approved.

[provokateurin]

Had to rebase due to #57667 adding a test that was failing now.

[provokateurin]

/backport to stable33

[provokateurin]

/backport to stable32

[provokateurin]

/backport to stable31

[provokateurin]

/backport to stable30

[provokateurin]

/backport to stable29

[backportbot]

The backport to stable30 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable30
git pull origin stable30

# Create the new backport branch
git checkout -b backport/58689/stable30

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 045ad432 5dbbe2cc

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/58689/stable30

Error: Failed to check for changes with origin/stable30: No changes found in backport branch

---

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

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/58689/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 045ad432 5dbbe2cc

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/58689/stable29

Error: Failed to check for changes with origin/stable29: No changes found in backport branch

---

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