Goes with JuliaLang/julia#55040

Co-authored-by: Claire Foster <aka.c42f@gmail.com>

This case is ambiguous as it might be either one of the following;
require the user to explicitly disambiguate between them

```
function (@f(x),)
    body
end

function @f(x)
    body
end
```

For the same reasons, `function ($f) body end` is also ambiguous.

Also fix parsing of `function (f(x),) end` to correctly emit a tuple.