Add a type param to Listener interface

[jodinathan]

Today the TlsListener extends Listener and AsyncIterable<TlsConn>.
The problem is that Listener already extends AsyncIterable<Conn>:

export interface TlsListener extends Listener, AsyncIterable<TlsConn> { }
export interface Listener extends AsyncIterable<Conn> { }

Can we change the Listener so it has a type param so then we can remove the AsyncIterable<TlsConn> from TlsListener?

ie:

export interface Listener<T extends Conn = Conn> extends AsyncIterable<T> {}

export interface TlsListener extends Listener<TlsConn> {}

I would PR this but I couldn't find it in any d.ts file

[petamoriken]

Here!
https://github.com/denoland/deno/blob/25aac6c7a8e015c24966168d0e3897849fefc68a/ext/net/lib.deno_net.d.ts