Fixes#24868
The writable mask was a bit misleading. We should wrap with the
sharepermissions (as they are used everywhere else). The
PERMISSIONS_SHARE are added since that is required for the public link
check plugin.
WebDAVFS as used by Finder requires a Class 2 compatible WebDAV server. This change introduces a fake locking provider which will simply advertise Locking support when a request originates from WebDAVFS. It will also return successful LOCK and UNLOCK responses.