Implement wasi-http serving.

[brendandburns]

cc @achille-roussel

This implements HTTP serving in the wasi-http specification. It enables wasi-run to act as an HTTP server for web assembly.

Let me know if you'd prefer that this was in a different binary.

There are C and Go examples.

[achille-roussel]

The change looks good, thanks for adding tests!

I'm OK with adding options on wasirun to exercise the features supported in this package 👍

I'm curious about the new types module that this PR introduces, do you know if it is described somewhere a specification, or is there another runtime implementing it?

[brendandburns]

The types module is defined in this WIT file:

https://github.com/WebAssembly/wasi-http/blob/main/wit/types.wit

Note that the fact that it is called types is actually due to a bug in the wit-bindgen tool which didn't use namespaces correctly.

When we revise this forward to be a v2 the name of this module will move to
wasi::http::

[brendandburns]

Just for context, there is an intersection between the wit files, the wit-bindgen tool and the guest SDK that is used to access the functionality.

I will send a PR to improve the documentation of how this works.

[achille-roussel]

Thanks for the explanations!