Add a new Eshell special reference type for markers

Add a new Eshell special reference type for markers

* lisp/eshell/esh-arg.el (eshell-get-marker, eshell-insert-marker)
(eshell-complete-marker-ref): New functions...
(eshell-special-ref-alist): ... Add them to the new "marker" entry.

* test/lisp/eshell/esh-arg-tests.el
(esh-arg-test/special-reference/marker)
(esh-arg-test/special-reference/nested)
(esh-arg-test/special-reference/lisp-form):
* test/lisp/eshell/em-cmpl-tests.el
(em-cmpl-test/special-ref-completion/type)
(em-cmpl-test/special-ref-completion/marker): New tests.

* doc/misc/eshell.texi (Arguments): Document the new special ref type.

* etc/NEWS: Announce this change (bug#66458).