Revert "Remove the need for HostRef<Module> (#778)"

This reverts commit 7b33f1c619.

Pushed a few extra commits by accident, so reverting this.

crates/api/tests/traps.rs

@@ -15,16 +15,17 @@ fn test_trap_return() -> Result<(), String> {
     let store = Store::default();
     let binary = parse_str(
         r#"
-            (module
-            (func $hello (import "" "hello"))
-            (func (export "run") (call $hello))
-            )
-        "#,
+                (module
+                (func $hello (import "" "hello"))
+                (func (export "run") (call $hello))
+                )
+            "#,
     )
     .map_err(|e| format!("failed to parse WebAssembly text source: {}", e))?;
 
-    let module =
-        Module::new(&store, &binary).map_err(|e| format!("failed to compile module: {}", e))?;
+    let module = HostRef::new(
+        Module::new(&store, &binary).map_err(|e| format!("failed to compile module: {}", e))?,
+    );
     let hello_type = FuncType::new(Box::new([]), Box::new([]));
     let hello_func = HostRef::new(Func::new(&store, hello_type, Rc::new(HelloCallback)));