DMN16 — FunctionItem `parameters` array attribute is plural, not singular in name

The `parameters` attribute of the new FunctionItem introduced in DMN 1.3 is plural in name and not singular like all other array attributes described in the meta-models. This is an exception.

This leads to an XML form where each `<parameters>` element contains one parameter.

Recommendation. Change FunctionItem array attribute `parameters` to `parameter`. Another possibility is to deprecate `parameters` in favour of `parameter` and drop support in a future version.