bdx: Fix byte compilation on Emacs<29

* bdx.el (bdx--ivy-display-transformer): Use `split-string' instead of
new `string-split'.

Author: mkcms

bdx.el

@@ -521,7 +521,7 @@ This turns a string of the form \\='function<type<T>>\\=' into
                         demangled
                       (bdx--untemplatize-string demangled))
                   name)))
-           (dolist (word (string-split ivy-text))
+           (dolist (word (split-string ivy-text))
              (when (ignore-errors
                      (let ((case-fold-search t))
                        (string-match word line)))