New minor mode 'minibuffer-regexp-mode'

New minor mode 'minibuffer-regexp-mode'

This mode is for editing regexps in minibuffer, it highlights
parens via `show-paren-mode' and `blink-matching-paren' in a
user-friendly way, avoids reporting false paren mismatches,
and makes sexp navigation more intuitive.
* lisp/minibuffer.el (minibuffer-regexp-mode)
(minibuffer--regexp-primed, minibuffer--regexp-prompt-regexp):
New variables.
(minibuffer--regexp-propertize, minibuffer--regexp-primed)
(minibuffer--regexp-before-change)
(minibuffer--regexp-after-change)
(minibuffer--regexp-post-self-insert, minibuffer--regexp-setup)
(minibuffer--regexp-exit, minibuffer-regexp-mode): New functions.
(minibuffer-regexp-prompts): New option.

* doc/lispref/minibuf.texi (Minibuffer Misc): Document the new
mode and its option.

* etc/NEWS: Announce the new mode.

Bug#50766