bug#31807: 27.0; `info-apropos' bad name or bad matching

[Drew Adams <drew.adams@oracle.com>]

I threw this together quickly, as a POC.  It does the job, but
probably we can do even better.  (The doc string would at least
need to be beefed up, to describe the input and search behavior.)

(defun info-apropos (pattern)
  "Grovel indices of all known Info files on your system for apropos PATTERN.
Build a menu of the possible matches."
  (interactive (list (apropos-read-pattern "index entries")))
  (apropos-parse-pattern pattern)
  (if (equal apropos-regexp "")
      (Info-find-node Info-apropos-file "Top")
    (let ((nodes  Info-apropos-nodes)
          nodename)
      (while (and nodes  (not (string-match apropos-regexp (nth 1 (car nodes)))))
        (setq nodes  (cdr nodes)))
      (if nodes
          (Info-find-node Info-apropos-file (caar nodes))
        (setq nodename  (format "Index for '%s'" apropos-regexp))
        (push (list nodename apropos-regexp (Info-apropos-matches apropos-regexp))
              Info-apropos-nodes)
        (Info-find-node Info-apropos-file nodename)))))

BTW, should the name be `Info-apropos' or `info-apropos'?