bug#31953: feature request - `highlight-rx` interactively

[Juri Linkov <juri@linkov.net>]

> Towards the transition to rx from regexp
> may I suggest `highlight-rx` for `highlight-regexp`.
>
> A usecase is to mark a region or string of few words
> and to call `highlight-rx` which does a verbatim highlight.

Nothing stops you from using rx in regexp commands already.

The first example shows how to use rx to find all Lisp comments:

 M-s o      ;; occur
 M-:        ;; eval-expression, then type or yank the following rx:
 (insert (rx bol (* whitespace) ";" (* nonl)))
 <return>   ;; exit-minibuffer inserts the converted regexp to the minibuffer
 <return>   ;; exit-minibuffer uses this regexp

The second example shows how to use rx to remove all Lisp comments:

 C-M-%      ;; query-replace-regexp
 M-:        ;; eval-expression
 M-p        ;; previous-history-element inserts the previous rx from history
 <return>   ;; exit-minibuffer inserts the converted regexp to the minibuffer
 <return>   ;; exit-minibuffer uses an empty string as replacement
 <return>   ;; exit-minibuffer replaces all comments with empty string

in 'emacs -Q' with (setq enable-recursive-minibuffers t)
The same can be used for 'highlight-regexp' as well.