get-file-list in Dialogs

Like get-file, except that the user can select multiple files, and the result is either a list of file paths of #f.

• (get-file-list message parent directory filename extension style filters) -> list of paths or #f
   message = #f : string or #f
   parent = #f : frame% or dialog% object or #f
   directory = #f : path or #f
   filename = #f : path or #f
   extension = #f : string or #f
   style = null : an empty list of symbols
     filters = '(("Any" "*.*")) : list of 2-string lists