Pass kwargs through to `get_function_sql`

[mvanderlee]

kwargs are passed around everywhere except in Function.get_sql.

I've implemented a parameter wrapper to ensure I can build parametrized queries, but this doesn't work on functions because of this simple issue.

https://github.com/kayak/pypika/blob/master/pypika/terms.py#L1336

[mvanderlee]

This also requires a change to Function.get_function_sql to prevent duplicate kwargs:

get_function_sql(self: Function, subquery: Any = None, with_alias: Any = None, **kwargs: Any) -> str:
    special_params_sql = self.get_special_params_sql(**kwargs)

    return "{name}({args}{special})".format(
        name=self.name,
        args=",".join(
            p.get_sql(with_alias=False, subquery=True, **kwargs)
            if hasattr(p, "get_sql")
            else self.get_arg_sql(p, **kwargs)
            for p in self.args
        ),
        special=(" " + special_params_sql) if special_params_sql else "",
    )

[wd60622]

Would you like to make a PR?

[mvanderlee]

Gladly, done.