Minor changes for components related to wit-bindgen support (#5053)

* Plumb type exports in components around more

This commit adds some more plumbing for type exports to ensure that they
show up in the final compiled representation of a component. For now
they continued to be ignored for all purposes in the embedding API
itself but I found this useful to explore in `wit-bindgen` based tooling
which is leveraging the component parsing in Wasmtime.

* Add a field to `ModuleTranslation` to store the original wasm

This commit adds a field to be able to refer back to the original wasm
binary for a `ModuleTranslation`. This field is used in the upcoming
support for host generation in `wit-component` to "decompile" a
component into core wasm modules to get instantiated. This is used to
extract a core wasm module from the original component.

* FIx a build warning

crates/environ/src/component/dfg.rs

@@ -152,6 +152,7 @@ pub enum Export {
     ModuleStatic(StaticModuleIndex),
     ModuleImport(RuntimeImportIndex),
     Instance(IndexMap<String, Export>),
+    Type(TypeDef),
 }
 
 /// Same as `info::CoreDef`, except has an extra `Adapter` variant.
@@ -430,6 +431,7 @@ impl LinearizeDfg<'_> {
                     .map(|(name, export)| (name.clone(), self.export(export)))
                     .collect(),
             ),
+            Export::Type(def) => info::Export::Type(*def),
         }
     }