feat(wit-bindgen): relax Sized bound on Host traits (#6117)

This allows to use implementations as trait objects
(e.g. `Box<dyn myiface::Host>`)

Signed-off-by: Roman Volosatovs <roman@profian.com>

crates/wit-bindgen/src/lib.rs

@@ -992,7 +992,7 @@ impl<'a> InterfaceGenerator<'a> {
         }
         // Generate the `pub trait` which represents the host functionality for
         // this import.
-        uwriteln!(self.src, "pub trait Host: Sized {{");
+        uwriteln!(self.src, "pub trait Host {{");
         for (_, func) in iface.functions.iter() {
             self.generate_function_trait_sig(owner, func);
         }