[IMP] hooks: improve useRef typings

With this commit, we can get the type for the target component for a
ref.

By default, if the generic type is not given, the ref will simply use
the base Component type.

tests/hooks.test.ts

@@ -267,7 +267,7 @@ describe("hooks", () => {
     class WidgetC extends Component {
       static template = xml`<div class="outer-div">Hello<WidgetB t-ref="mywidgetb" /></div>`;
       static components = { WidgetB };
-      ref = useRef("mywidgetb");
+      ref = useRef<WidgetB>("mywidgetb");
     }
 
     const widget = new WidgetC();