Allow omitting name while creating dynamic workers

[ketanhwr]

No description provided.

[github-actions]

The generated output of @cloudflare/workers-types matches the snapshot in types/generated-snapshot 🎉

[penalosa]

Feel free to ignore this, but what about allowing env.loader.get(loadCodeCallback).getEntrypoint()?

[kentonv]

The original version of this PR reversed the ordering of the params to make the param optional, but that was a breaking change.

But we could, perhaps, create an "overloaded" interface, which accepts either (id, func) or (func). But overloads are kind of awkward.

And actually, if you think about it, when the ID is null, then there's no need for a callback. The callback will always be called, so instead we should just let you pass in the worker definition instead of a callback.

So maybe what we really want is a new method like: load(code)

Which is logically equivalent to: get(null, () => code)

Either way I think passing null to get() should be supported. But probably we want to add this new load() method as well.

[ketanhwr]

Oops, looks like the one-off ephemeral isolates aren't behaving well with asan
*** Fatal uncaught kj::Exception: workerd/server/server.c++:302: failed: expected !service.value->isShared(); service still has references after unlinking; service.key = worker-loader-test. Let me see

Should be fixed now