Handle file-notify callbacks

[lastquestion]

hat-tip to @yyoncho

file-notify-add-watch is a compiled Lisp function in ‘filenotify.el’.

(file-notify-add-watch FILE FLAGS CALLBACK)
....
When any event happens, Emacs will call the CALLBACK function passing
it a single argument EVENT, which is of the form

  (DESCRIPTOR ACTION FILE [FILE1])

• Verify how filenotify calls the callback. I suspect it's from C code.
• Figure out what to advise to wrap the callback, handle similarly to timers or process filters

lsp might be a good test case for this.

[lastquestion]

File notifications are handled correctly because keyboard.c calls command-execute and ultimately that calls call-interactively which is caught by #42. But we should do better and capture the timer so we know exactly which callback IS going to get called. Function to advise is file-notify-add-watch.