Implement TypeHandlerRegistry

[jasnell]

Provides a mechanism to obtain const TypeHandler& references without needing to inject them via jsg argument injection.

tests were implemented by claude with a bit of manual intervention.

This approach is imperfect, of course... specifically because it requires individual types to be registered. It won't automatically work for things like const TypeHandler<jsg::Promise<T>> since it can't know about all possible jsg::Promise<T>'s we might use, but it's good enough to investigate the utility.

** THIS IS CURRENTLY JUST AN EXPLORATION OF OPTIONS **

Draft since this is still WIP/being investigate.

Internal build will fail until the same v8 patch is landed there.

[github-actions]

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

[kentonv]

Awkward thing here is how do you specify what types you need to be registered, so that they are in the registry when you look them up? The parameter injection approach nicely solves that because the JSG "linker" (stuff that happens in the giant template instantiation in workerd-api.c++) sees every injected parameter and can make sure the associated types get instantianted.

But we could reasonably support a registry of all wrapped types, at least. In fact I think we already sort of have one -- resourceTypeMap.

I think we could use resourceTypeMap to support two new methods on jsg::Lock that specifically operate on JSG_RESOURCE_TYPE types:

template <typename T>
JsObject Lock::wrapApiType(Ref<T> ref);

template <typename T>
kj::Maybe<Ref<T>> Lock::tryUnwrapApiType(JsValue val);

Those could replace a lot of TypeHandler usage.

[jasnell]

Closing... experiment done. Yes, this helps a few things but it's rather cumbersome.