Rebind in read-regexp-map ‘M-c’ to ‘M-s c’ compatible with search-map

Rebind in read-regexp-map ‘M-c’ to ‘M-s c’ compatible with search-map

Also it's compatible with 'M-s c' (isearch-toggle-case-fold)
used during Isearch.  Also makes possible to use the global keybinding
'M-c' (capitalize-dwim) in the minibuffer.

* doc/lispref/minibuf.texi (Text from Minibuffer): Rename ‘M-c’ to ‘M-s c’.

* lisp/replace.el (read-regexp-map): Rebind ‘M-c’ to ‘M-s c’ (bug#60741).
(read-regexp-toggle-case-fold): Rename from read-regexp-toggle-case-folding
to more standard name.