bug#36767: 26.1; request: add more quick keys to the *Help* buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: larsi@gnus.org,  36767@debbugs.gnu.org,  emacsuser@freemail.hu
> Date: Fri, 18 Jun 2021 22:14:05 +0300
> 
> >> it would be possible to type just 'C-h v RET c' to customize it.
> >
> > You forget the need to switch to the *Help* buffer before typing 'c',
> > don't you?
> 
> I have no such problems because of using windmove-display-*
> commands where the prefix arg defines whether to select
> the displayed window or not.

What does windmove have to do with this?

> > So how about some special prefix key and a keymap to allow invoking
> > these commands from a buffer other than *Help*?
> 
> To look at the source of a function, a quicker key is `M-.'
> or `C-u M-.' that reads a symbol name.

That doesn't work well with cross-links in the doc strings, because
you need to type the name of the symbol.  I want a command that will
do the equivalent of TAB in the Help buffer, but which will work from
another buffer.

> +*** New command 'help-customize' ('c').
> +This command will customize the variable or the face (if any).

I think this should make it clear the variable/face are those whose
doc string is being shown in *Help*.