Introduce `file-notify-valid-p'

Introduce `file-notify-valid-p'

* lisp/filenotify.el (file-notify-valid-p): New defun.
(gfile-valid-p, w32notify-valid-p): Make them an alias to `identity'.

* lisp/net/tramp-adb.el (tramp-adb-file-name-handler-alist)
* lisp/net/tramp-gvfs.el (tramp-gvfs-file-name-handler-alist)
* lisp/net/tramp-sh.el (tramp-sh-file-name-handler-alist)
* lisp/net/tramp-smb.el (tramp-smb-file-name-handler-alist)
<file-notify-valid-p>: Add handler.

* lisp/net/tramp.el (tramp-file-name-for-operation):
Add `file-notify-valid-p'.
(tramp-handle-file-notify-valid-p): New defun.

* src/inotify.c (Finotify_valid_p): New defun.
(syms_of_inotify): Declare Sinotify_valid_p.