Use `isearch-search-fun' in `perform-replace' (bug#10885, bug#10887).

Use `isearch-search-fun' in `perform-replace' (bug#10885, bug#10887).

* lisp/replace.el (replace-search-function)
(replace-re-search-function): Set default values to nil.
(perform-replace): Let-bind isearch-related variables based on
replace-related values, call `isearch-search-fun' and let-bind
the result to `search-function'.  Remove code that sets
`search-function' and `search-string' separately for
`delimited-flag'.
(replace-highlight): Add new argument `delimited-flag' and
rename other arguments to the names used in `perform-replace'.
Let-bind `isearch-word' to the argument `delimited-flag'.