Backport expansion of Time Stamp documentation

Backport expansion of Time Stamp documentation

* doc/emacs/files.texi (Time Stamps): Add examples of enabling
time stamping with add-hook, setting time-stamp-pattern as a
file-local variable, and showing a time stamp at the end of a
file.  Divide into three sections.
* doc/emacs/emacs.texi: Add new nodes to menu.
* lisp/info.el (Info-file-list-for-emacs): Remove entry that
points Info at time-stamp discussion in the Autotype document.
* lisp/time-stamp.el (time-stamp-format, time-stamp-active,
time-stamp-count, time-stamp-pattern, time-stamp, time-stamp-string):
Expand doc strings.  Include Info cross-references.

Cherry picked from commits on the main branch.
Do not merge to master.