wit-component: clean up type exports.

This commit refactors encoding in `wit-component` to only export types from the
default interface and stop exporting types from instance types used in imports.

It also makes "type only" encodings more explicit with `InterfaceEncoder` that
will encode the types from a single interface only.

Author: Peter Huene

crates/wit-component/src/cli.rs

@@ -3,7 +3,8 @@
 #![deny(missing_docs)]
 
 use crate::{
-    decode_interface_component, encoding::ComponentEncoder, InterfacePrinter, StringEncoding,
+    decode_interface_component, ComponentEncoder, InterfaceEncoder, InterfacePrinter,
+    StringEncoding,
 };
 use anyhow::{bail, Context, Result};
 use clap::Parser;
@@ -146,9 +147,7 @@ impl WitToWasmApp {
 
         let interface = parse_interface(None, &self.interface)?;
 
-        let encoder = ComponentEncoder::default()
-            .interface(&interface)
-            .types_only(true);
+        let encoder = InterfaceEncoder::new(&interface).validate(true);
 
         let bytes = encoder.encode().with_context(|| {
             format!(