Isearch hit count. (Bug#29321)

Isearch hit count.  (Bug#29321)

* lisp/isearch.el (isearch-lazy-count): New defcustom.
(lazy-count): New defgroup.
(lazy-count-prefix-format, lazy-count-suffix-format): New defcustom.
(isearch-lazy-count-format): New function.
(isearch-message-prefix, isearch-message-suffix): Use it.
(isearch-lazy-highlight-window-start-changed)
(isearch-lazy-highlight-window-end-changed)
(isearch-lazy-count-current, isearch-lazy-count-total)
(isearch-lazy-count-hash): New variables.
(isearch-lazy-highlight-new-loop): Reset isearch-lazy-count-total
and update isearch-lazy-count-current for isearch-message.
(isearch-lazy-highlight-update): Run full-buffer loop for
isearch-lazy-count.
(isearch-lazy-highlight-buffer-update): Count isearch-lazy-count-total.
Set isearch-lazy-count-current at the end.