Performance regression in 31 with co-owner shares

[icewind1991]

The co-owner shares introduced in #49073 causes a performance regression as mentioned in #49073 (review) due it it now having to query shares for each file in a folder.

Possible solution would be:

• create a new extension interface to allow listing shares in a folder without the sharee filter
• for any 3rd party share backend not implementing the new interface, just fall back to disabling co-owners