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

[Juri Linkov]

>> 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:
>
> That is, some faces have odd sizes, so the completion display may look a
> bit odd.
>
> But it does accurately tell you what the result is doing to be, so
> perhaps it's OK?  Anybody have any opinions?

Whereas highlight-regexp can use all faces, the preferable faces are in
hi-lock-face-defaults, so they need to be displayed separately.