Introduce own method for calendar unsharing

[kesselb]

• Resolves: [Bug]: (CalDav|CardDav) unsharing calendar as owner leads to wrong state #49834
• Resolves: [Bug]: Individual calendar share removal leads to group unshare #49907

Summary

I'm sorry the PR ended up being much larger than expected. The issue arose because managing calendar shares as an owner and unsharing a calendar as an owner used the same code. This led to a situation where removing an individual calendar share as an owner, while having at least one group share, created an unshare item for the individual user and made the calendar inaccessible.

I reworked the implementation to use a separate method for unsharing a user and reverted the changes for the "manage shares as calendar owner" method. We decided to implement an occ command to unset calendar unshares instead of a migration that drops all unshares. Additionally, there's now a command to list the calendar shares.

The second commit is a hardening of the unsharing logic. Previously, we considered all principal URIs (users, groups, and circles) when looking for unshares. Now, it only considers the user's principal URI, as we only support unshares for individuals but not for groups or teams yet.

Steps to reproduce are available at: #49834

The events are, among other things, used to write the activity, so please keep an eye on whether the activities look correct while testing.

TODO

• Review
• Check CardDav
• CI
• Backports

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[kesselb]

owner-displayname is only set if we have displayname:

server/apps/dav/lib/CalDAV/CalDavBackend.php

Lines 3522 to 3535 in 2ea3491

	private function addOwnerPrincipalToCalendar(array $calendarInfo): array {
	$ownerPrincipalKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal';
	$displaynameKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}owner-displayname';
	if (isset($calendarInfo[$ownerPrincipalKey])) {
	$uri = $calendarInfo[$ownerPrincipalKey];
	} else {
	$uri = $calendarInfo['principaluri'];
	}
	$principalInformation = $this->principalBackend->getPrincipalByPath($uri);
	if (isset($principalInformation['{DAV:}displayname'])) {
	$calendarInfo[$displaynameKey] = $principalInformation['{DAV:}displayname'];
	}
	return $calendarInfo;

But we use it without an isset before and thus, marking it as optional, will trigger some new psalm warnings.

[ChristophWurst]

@SebastianKrupinski please test and review this PR. Thanks!

[SebastianKrupinski]

Tested Works.

[kesselb]

/backport to stable31