Change `wordify' to `word-search-regexp'.

Change `wordify' to `word-search-regexp'.

* lisp/isearch.el (isearch-occur): Use `word-search-regexp' for
`isearch-word'.
(isearch-search-and-update): Add condition for `isearch-word' and
call `word-search-regexp'.

* src/search.c (Fword_search_regexp): New Lisp function created from
`wordify'.  Change type of arg `lax' from `int' to `Lisp_Object'.
(Fword_search_backward, Fword_search_forward)
(Fword_search_backward_lax, Fword_search_forward_lax):
Use `Fword_search_regexp' instead of `wordify'.  Doc fix.
(syms_of_search): Define `Sword_search_regexp'.

Fixes: debbugs:10145