Add support for nested namespaces and packages

[ouillie]

This tracks support for the 🪺-gated feature in the WIT spec (nested package namespaces and names).

Related:

• Package namespaces and package names are not generatable in combination wit-bindgen#1224
• Package declaration syntax clarity WebAssembly/component-model#549

I'm working on a rough draft to address this in wasm-tools. Happy for any feedback on the approach so far. In particular, I don't understand what a "projection" is or how this might interact / interfere with this design. I'm also wondering about the TODO I noted here, where a key in the encoding map appears to use the syntax package:namespace:package/name/interface-name/function-name, which I fear might introduce an ambiguity. Perhaps nested package names should use a different separator other than /, like ..

[alexcrichton]

Thanks for this! One thing I'll caution though is that this is going to have a pretty deep impact on the wit-parser AST and structures. This affects not only this repository but all downstream code generators as well for example (e.g. wit-bindgen). In that sense the core design decisions here have quite a wide reaching impact so we'll want to make sure that everything is nailed down and expects the usage of downstream generators.

There's also a bit of an open question about how exactly to model all of this in WIT. For example there's been the historical idea of a nest keyword where an interface can be included inside of another. Implementing that I believe would be quite the project to take on and also likely require resolving some preexisting tech debt in the design of the AST right now too.

I'm at least personally stretched pretty thin right now so I don't have much bandwidth to help with the design here unfortunately. This is also unfortunately likely not an easy project to take on due to the size and scale of the change being made here. I don't mean to dissuade you though! I want to be sure to set expectations though