feat(serve): support export default class

[marvinhagemeister]

This PR adds support for passing a class instance for deno serve export default fetch.

class Foo implements Deno.ServeDefaultExport {
  fetch(_request: Request) {
    return new Response("Hello world!");
  }
}

export default new Foo();

Fixes #24062

[dsherret]

I'm not sure it makes sense to support a class declaration here like:

export default class Foo implements Deno.ServeDefaultExport {
  fetch(_request: Request) {
    return new Response("Hello world!");
  }
}

...because generally classes are used to inject stuff in the constructor then pass around the instances. So practically someone would probably do something like:

const someInstance = new Foo(...some args here...);

// then
export default someInstance;

...which seems to be all that's necessary for #24062 ?

[marvinhagemeister]

@dsherret fair point, dropped that from the PR so that only class instances are supported.

[dsherret]

Maybe let's try updating this test to use something on the instance? For example, something like:

class Foo implements Deno.ServeDefaultExport {
  message = "Hello world!";
  fetch(_request: Request) {
    return new Response(this.message);
  }
}

I think right now it will not work because we need to bind the function to the instance.