CalDavBackend.getCalendarsForUser is executed twice when listing the user's calendar

Idea

We know in AppCalendarPlugin.getWrappedCalendars, that we don't care about the calendars from the default backends.
Add a third parameter "skipCalendarProvider" to OC\Calendar\Manager.getCalendarsForPrincipal to skip the default calendar providers.

Reproduce

Set a breakpoint:
https://github.com/nextcloud/server/blob/28ec9c7e80e825aea2537f865e2862aecf25c8f1/apps/dav/lib/CalDAV/CalDavBackend.php#L299

Run:

curl -X PROPFIND "https://admin:admin@server.internal/remote.php/dav/calendars/admin/" \
    -H "Content-Type: application/xml" \
    -H "Cookie: XDEBUG_SESSION=PHPSTORM" \
    -d '<?xml version="1.0"?>
<x0:propfind xmlns:x0="DAV:">
	<x0:prop>
		<x0:current-user-privilege-set/>
		<x0:displayname/>
		<x0:getcontenttype/>
		<x0:getetag/>
		<x0:owner/>
		<x0:resourcetype/>
		<x0:sync-token/>
		<x1:calendar-availability xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:calendar-description xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:calendar-free-busy-set xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:calendar-timezone xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:max-attendees-per-instance
				xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:max-date-time xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:max-instances xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:max-resource-size xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:min-date-time xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:schedule-calendar-transp xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:schedule-default-calendar-URL
				xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:supported-calendar-component-set
				xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x1:supported-calendar-data xmlns:x1="urn:ietf:params:xml:ns:caldav"/>
		<x3:deleted-at xmlns:x3="http://nextcloud.com/ns"/>
		<x3:owner-displayname xmlns:x3="http://nextcloud.com/ns"/>
		<x3:trash-bin-retention-duration xmlns:x3="http://nextcloud.com/ns"/>
		<x4:calendar-enabled xmlns:x4="http://owncloud.org/ns"/>
		<x4:invite xmlns:x4="http://owncloud.org/ns"/>
		<x5:allowed-sharing-modes xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:getctag xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:publish-url xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:source xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:subscribed-strip-alarms xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:subscribed-strip-attachments
				xmlns:x5="http://calendarserver.org/ns/"/>
		<x5:subscribed-strip-todos xmlns:x5="http://calendarserver.org/ns/"/>
		<x6:calendar-color xmlns:x6="http://apple.com/ns/ical/"/>
		<x6:calendar-order xmlns:x6="http://apple.com/ns/ical/"/>
		<x6:refreshrate xmlns:x6="http://apple.com/ns/ical/"/>
	</x0:prop>
</x0:propfind>'

Stop 1:

CalDavBackend.php:299, OCA\DAV\CalDAV\CalDavBackend->OCA\DAV\CalDAV\{closure:/var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php:298-480}()
TTransactional.php:45, OCA\DAV\CalDAV\CalDavBackend->atomic()
CalDavBackend.php:298, OCA\DAV\CalDAV\CalDavBackend->getCalendarsForUser()
CalendarHome.php:85, OCA\DAV\CalDAV\CalendarHome->getChildren()
Plugin.php:184, OCA\DAV\DAV\Sharing\Plugin->propFind()
WildcardEmitterTrait.php:89, Sabre\DAV\Server->emit()
Server.php:1052, Sabre\DAV\Server->getPropertiesByNode()
Server.php:984, Sabre\DAV\Server->getPropertiesIteratorForPath()
Server.php:1664, Sabre\DAV\Server->writeMultiStatus()
Server.php:1649, Sabre\DAV\Server->generateMultiStatus()
CorePlugin.php:347, Sabre\DAV\CorePlugin->httpPropFind()
WildcardEmitterTrait.php:89, Sabre\DAV\Server->emit()
Server.php:472, Sabre\DAV\Server->invokeMethod()
Server.php:48, OCA\DAV\Connector\Sabre\Server->start()
Server.php:395, OCA\DAV\Server->exec()
remote.php:21, require_once()
remote.php:145, {main}()

Stop 2:

CalDavBackend.php:299, OCA\DAV\CalDAV\CalDavBackend->OCA\DAV\CalDAV\{closure:/var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php:298-480}()
TTransactional.php:45, OCA\DAV\CalDAV\CalDavBackend->atomic()
CalDavBackend.php:298, OCA\DAV\CalDAV\CalDavBackend->getCalendarsForUser()
CalendarProvider.php:28, OCA\DAV\CalDAV\CalendarProvider->getCalendars()
Manager.php:174, OC\Calendar\Manager->OC\Calendar\{closure:/var/www/html/lib/private/Calendar/Manager.php:163-175}()
Manager.php:163, array_map()
Manager.php:163, OC\Calendar\Manager->getCalendarsForPrincipal()
AppCalendarPlugin.php:52, OCA\DAV\CalDAV\AppCalendar\AppCalendarPlugin->getWrappedCalendars()
AppCalendarPlugin.php:34, OCA\DAV\CalDAV\AppCalendar\AppCalendarPlugin->fetchAllForCalendarHome()
CalendarHome.php:118, OCA\DAV\CalDAV\CalendarHome->getChildren()
Plugin.php:184, OCA\DAV\DAV\Sharing\Plugin->propFind()
WildcardEmitterTrait.php:89, Sabre\DAV\Server->emit()
Server.php:1052, Sabre\DAV\Server->getPropertiesByNode()
Server.php:984, Sabre\DAV\Server->getPropertiesIteratorForPath()
Server.php:1664, Sabre\DAV\Server->writeMultiStatus()
Server.php:1649, Sabre\DAV\Server->generateMultiStatus()
CorePlugin.php:347, Sabre\DAV\CorePlugin->httpPropFind()
WildcardEmitterTrait.php:89, Sabre\DAV\Server->emit()
Server.php:472, Sabre\DAV\Server->invokeMethod()
Server.php:48, OCA\DAV\Connector\Sabre\Server->start()
Server.php:395, OCA\DAV\Server->exec()
remote.php:21, require_once()
remote.php:145, {main}()

https://github.com/nextcloud/server/blob/28ec9c7e80e825aea2537f865e2862aecf25c8f1/apps/dav/lib/CalDAV/AppCalendar/AppCalendarPlugin.php#L50-L57

Start with apps/dav/lib/CalDAV/AppCalendar/AppCalendarPlugin.php, lib/private/Calendar/Manager.php, and apps/dav/lib/CalDAV/CalendarProvider.php, following the getCalendarsForPrincipal call shown in the stack trace. Reproduce with the provided PROPFIND request and breakpoint in CalDavBackend.php:299; done means the default calendar providers can be skipped for this path so getCalendarsForUser is not executed twice.