Slightly extending NOTE_EXTEND

[Theodore Preduta <theo%pta.gg@localhost>]

I was looking into the locking issues pointed out in the Linux inotify
emulation I wrote (see
https://mail-index.netbsd.org/source-changes-d/2023/08/25/msg014056.html),
and I think it can simultaneously be made much simpler and solve the
locking problems if extra context is provided through kevent.  To do
this I propose to

1. add a void * parameter to filterop::f_event (and also to knote(),
VN_KNOTE(), etc.), mostly to pass in the relevant componentname; and

2. send a NOTE_EXTEND event during a rename (in addition to the
NOTE_WRITE) in both the source and destination directories if the source
and destination directories differ.  Note that this is not an original
extension, FreeBSD's NOTE_EXTEND does this.

Does this seem sane and/or do we want the change to NOTE_EXTEND?

Theo(dore)