bug#44895: Add Info-copy-permalink

[Drew Adams]

If you use Info+ then `G' (`Info-goto-node-web')
takes you to the Web version of the current node.

It uses function `Info-url-for-node' (also from
Info+) to get the URL for that.

,----
| Info-url-for-node is an interactive compiled Lisp function in
| ‘info+.el’.
| 
| (Info-url-for-node NODE)
| 
| Return a URL for NODE, a node in the GNU Emacs or Elisp manual.
| Alternatively, NODE can have the form (MANUAL)NODE, where MANUAL is
| "emacs" or "elisp" and NODE is the name of the node in that
| manual.  Empty NODE in (MANUAL) defaults to the `Top' node.
`----