New minor mode: `electric-block-comment-mode'

New minor mode: `electric-block-comment-mode'

This minor lets you automatically closing block comments after
typing `block-comment-start'.  Thus, typing "/*" in c-mode and
its derivatives automatically inserts "*/".  (Bug#77081)

* etc/NEWS: Add minor-mode item.
* lisp/electric.el
(electric-block-comment-post-self-insert-function): New function.
(electric-block-comment-mode): New minor mode definition.

(cherry picked from commit 989f9f01f731c0dd0382bad50f1c45894d69c3ea)