DMN18 — Missing FEEL functions to format dates and times

The FEEL functions format-number(value, formatString), format-date(value, formatString), and format-dateTime(value, formatString) are needed in practice and have already been implemented as extension by many vendors. They should therefore be standardized.

The following approaches for formatting should be considered:
https://www.baeldung.com/java-number-formatting
https://developer.mozilla.org/en-US/docs/Web/XML/XPath/Reference/Functions/format-number
https://docs.oracle.com/javase/8/docs/api/java/text/DecimalFormat.html
https://developer.mozilla.org/en-US/docs/Web/XML/XSLT/Reference/Element/decimal-format
https://queirozf.com/entries/python-number-formatting-examples
https://doc.rust-lang.org/std/fmt/