Add gloo-worker crate

[ranile]

Migrate yew-agent to gloo-worker

The code in this PR is moved from the Yew repository as of commit yewstack/yew@6f6519d. All the credits go to original code authors.

[futursolo]

This looks fine to me for migrating from yew-agent to gloo-worker.

However, as we don't have non-worker based "agents" anymore, I think the implementation could be revised to be more specialised to implement workers:

• Do we need Reach on the worker itself?
  If we remove Reach from the worker trait, then a worker can be spawned as any type and the type can be specified at the time it is created. (this also means that we can merge PublicWorker and PrivateWorker together.)
• Currently, the path of a worker is not dynamic (specified in name_of_resource). If we make it possible to specify the path at the time a worker is created, will it be easier to handle relative paths? (as well as whether a worker is defined as a ES module.)

[ranile]

I'm going to merge this then.
I agree with the changes. Do you want to PR those changes? If not, I think we should release this as 0.1 right now. The implementation revisions could come later (I don't really have the time to make these changes myself right now)

[futursolo]

Do you want to PR those changes?

Not at anytime soon. I already have a lot on my plate at this moment.