Add new function `lm-package-needs-footer-line`

Add new function `lm-package-needs-footer-line`

* lisp/emacs-lisp/lisp-mnt.el (lm-package-needs-footer-line):
Factor out new function...
* lisp/emacs-lisp/package.el (package-buffer-info): ...from here.
* lisp/emacs-lisp/lisp-mnt.el (lm-verify): Use above new function.
* test/lisp/emacs-lisp/lisp-mnt-tests.el
(lm-tests--lm-package-needs-footer-line/empty-dependencies)
(lm-tests--lm-package-needs-footer-line/old-version)
(lm-tests--lm-package-needs-footer-line/new-version):
New tests.

(cherry picked from commit c302c5fab0c8dee12e7b19925452871ddb09c0b2)