Display the exit code if the last command failed in Eshell

Display the exit code if the last command failed in Eshell

* lisp/eshell/esh-io.el (eshell-last-command-status): Make
buffer-local.

* lisp/eshell/em-prompt.el (eshell-prompt-function): Insert the exit
code if last command failed.

* test/lisp/eshell/em-prompt-tests.el (em-prompt-test/after-failure):
New test.
(em-prompt-test/next-previous-prompt-1)
(em-prompt-test/forward-backward-matching-input-1): Add a failing
command to tests.

* doc/misc/eshell.texi (Invocation): Document change.

* etc/NEWS: Announce change (bug#65604).