Clarify structure of file-attribute's device number

Clarify structure of file-attribute's device number

* doc/lispref/buffers.texi (Buffer File Name): Fix description of
buffer-file-number.

* doc/lispref/files.texi (File Attributes): Clarify type of device
number.  Describe file-attribute-file-number.  (Bug#58446)

* etc/NEWS: Mention file-attribute-file-number.

* lisp/files.el (buffer-file-number, file-attribute-device-number)
(file-attribute-collect): Fix docstring.
(file-attribute-file-number): New defsubst.
(find-buffer-visiting, find-file-noselect)
(set-visited-file-name, basic-save-buffer):
* lisp/startup.el (normal-top-level-add-subdirs-to-load-path):
* lisp/eshell/em-unix.el (eshell-shuffle-files): Use it.

* src/dired.c (Ffile_attributes): Fix docstring.