Feature/654 fix j4ts

[lgrignon]

The commit message isn't detailed enough, let me explain a bit more: This PR tries to enhance slightly main/core overload signature:

• Specify return type when possible (any type can be a problem now with TS, because (let x: any; x.method<T>(); // error)
• Use maximum number of type arguments for core overload which defaults to any, in order to avoid inconsistent type args specification in client code

[lgrignon]

J4TS generated + deployed with this commit: https://github.com/j4ts/j4ts/commit/af79c9c8ca8470d94c03e1ceb8eada79b3cdd241

J4TS examples fixed: https://github.com/lgrignon/j4ts-example/actions/runs/465968261