Repair step to remove orphaned share entries with no matching oc_filecache entry

[PVince81]

In some situations, possibly due to bugs, it can happen that oc_share entries are referencing file ids that have no matching entry in oc_filecache.

Such entries need to be cleared within a repair step.
Code from #7293 could be reused to do that for every update.

Slightly related to #7874

[PVince81]

• remove orphaned share entries with no matching entry in filecache
• remove share entries where the "parent" column does not match any other share

CC @schiesbn

[PVince81]

It looks like it is possible to create orphaned shares from the web UI using the steps from #6985

This means that a repair script isn't enough, but would need to be a cron job (but only if there is no proper fix for #6985)

[PVince81]

@schiesbn see previous comment

[PVince81]

@DeepDiver1975 setting to 8.1, it's about time we implemented this.
Please set to backlog if not acceptable.

[PVince81]

or 8.2 😉

[PVince81]

Note: make sure to check that item_type is either file or folder. We don't want to delete orphaned calendar/contacts by mistake.

[PVince81]

Fixed by #14676