Named parameters not support on dynamic template invocations.

I'm using stringtemplate 4.0.8.

I'm having a problem passing a named argument to a template which has been looked up in a dictionary. Here is the offending line of code:

```
public ( }; separator=", ">) {
```

With `(field=fields.(it))` passing field names to a template that has been looked up in a dictionary, so that fields can be rendered in different ways in different situations by substituting in different dictionaries.

On the cheat sheet, the documentation for `<(expr)(argument-list)>` says:

> The argument-list is a list of attribute expressions or attribute assignments where each assignment is of the form attribute=expr.

Making it quite clear that `attribute=expr` is allowed. This worked on StringTemplate 3, but does not appear to be working on 4.