fsnotify: pass object pointer and type to fsnotify mark helpers

Instead of passing fsnotify_connp_t, pass the pointer to the marked
object.

Store the object pointer in the connector and move the definition of
fsnotify_connp_t to internal fsnotify subsystem API, so it is no longer
used by fsnotify backends.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240317184154.1200192-6-amir73il@gmail.com>