(filesets-commands): Add commands for "Isearch" and

(filesets-commands): Add commands for "Isearch" and
"Isearch (regexp)".  Replace `query-replace' and `query-replace-regexp'
with `perform-replace' using `filesets-cmd-query-replace-regexp-getargs'.
(filesets-run-cmd): Call `fn' only once if it is `multi-isearch-files'
or `multi-isearch-files-regexp'.
(filesets-cmd-query-replace-getargs): Call standard function
`query-replace-read-args' to read `query-replace' arguments.
Add `multi-query-replace-map'.
(filesets-cmd-query-replace-regexp-getargs)
(filesets-cmd-isearch-getargs): New functions.