* lisp/json.el: Add pretty-print option.

* lisp/json.el: Add pretty-print option.
(json-encoding-separator, json-encoding-default-indentation)
(json--encoding-current-indentation, json-encoding-pretty-print)
(json-encoding-lisp-style-closings): New vars.
(json--with-indentation): New macro.
(json-encode-hash-table, json-encode-alist, json-encode-plist)
(json-encode-array): Use it to obey json-encoding-pretty-print.
(json-pretty-print-buffer, json-pretty-print): New commands.

Fixes: debbugs:12634