bug#53255: [External] : bug#53255: highlight-regexp should show faces with their properties applied when selecting a face

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

> > Like read-color shows the color names with their actual colors, the
> > selection of a face should also show the names with their properties
> > applied.
> 
> The patch below implements this, but it does lead to some strange
> effects:

Icicles has done this since 2007.  See here:

https://www.emacswiki.org/emacs/Icicles_-_Candidates_with_Text_Properties

(FWIW, I see this Note on that page:
   "2007-01-24 - RMS has agreed to fix Emacs in this
    way, so this will become possible in Emacs."
 AFAIK, that never happened.)
___

Whether face, color, etc. completion candidates are
shown as, or accompanied by, such propertized samples is
controlled by option `icicle-WYSIWYG-Completions-flag':

---8<-------

icicle-WYSIWYG-Completions-flag is a variable defined in `icicles-opt.el'.

Its value is "MMMM"

Documentation:
Non-nil means show candidates in `*Completions*' using WYSIWYG.
This has an effect only for completion of things like faces, fonts,
and colors.

For face and color candidates, the particular non-nil value determines
the appearance:

* If t, the candidate displays its meaning: WYSIWYG.
* If a string, the string is propertized and then appended to the
  candidate,  to serve as a color swatch.

Some commands might override a string value with different text.  This
is the case for `icicle-read-color-WYSIWYG', for instance: the color
swatch text is always the color's RGB code.

Note that, starting with Emacs 22, if this option is non-nil, then
command `describe-face' does not use `completing-read-multiple', since
that (non-Icicles) function does not support WYSIWYG candidates.

---8<-------