fdo#81038 Fixed FormulaTokenIterator to use std::vector instead of linked list

Change-Id: I09f9adfa52b64732cc6200a0dbeb6263435c7c07
Reviewed-on: https://gerrit.libreoffice.org/10565
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>