bug#49330: Customization buffer should also offer printing code snippets

[Eli Zaretskii <eliz@gnu.org>]

> From: 積丹尼 Dan Jacobson
>  <jidanni@jidanni.org>
> Date: Fri, 02 Jul 2021 22:16:02 +0800
> 
> The *Customize Face* buffer looks like:
> 
>   For help using this buffer, see Easy Customization in the Emacs manual.
> 
>   Operate on all settings in this buffer:
>   Revert...   Apply   Apply and Save
>   1^^^^^^^^^^^2^^^^^^^3^^^^^^^^^^^^^
> 
> OK, but add a fourth menu item:
> "Print code snippet" or
> "Just print code snippet" or just
> "Print"!
> 
> Else currently one must
> 1. cp .emacs-custom.el /tmp
> 2. click "Apply and Save"
> 3. exit emacs #as we are about to replace a dot file it uses.
> 4. diff /tmp .emacs-custom.el #obtain the code snippet.
> 5. mv /tmp/.emacs-custom ~
> 6. restart emacs
> Just to obtain the code snippet!

What is that "code snippet" that you'd like to see?  If you want to
see the effect of customizing the face, then the Customize Face buffer
includes a "[sample]" part, which dynamically shows the results of
your customizations.