bindgen: Emit component type in generated code

[lann]

There are cases where it would be helpful to have access to the component type associated with bindgen!ed code, like allowing component type checking without separate WIT bookkeeping or the creation of an engine/component/linker/store to test instantiation.

Guest wit-bindgen embeds this information in the component-type custom section for use by wasm-component-ld; I'd like to do something similar for wasmtime bindgen, roughly:

let encoded = wit_component::metadata::encode(
    resolve,
    world_id,
    wit_component::StringEncoding::UTF8,
    None,
)?;
uwriteln!(self.src, "pub const COMPONENT_TYPE: &[u8] = &{encoded:?};");

which would allow the host to reconstruct the component type:

let wit_component::metadata::Bindgen {
    resolve,
    world,
    ..
} = wit_component::metadata::decode(generated::bindings::COMPONENT_TYPE)?;

If there is a compelling reason for it this could be gated by a bindgen opt but the const will disappear if it doesn't get used so I'm not sure if that is necessary.

[pchickey]

That seems harmless enough, I guess?

Is there a straightforward way to get a wasmtime::component::types::Component out of the bindgen at the moment?