[IMP] component,qweb: props validation

We re-add the possibility to validate props when dev mode is active.
No change in the API right Now. The dev mode is activated via the
configure method of App class.

tests/components/basics.test.ts

@@ -750,7 +750,7 @@ describe("basics", () => {
       static template = xml`<span>abc<t t-if="props.flag">def</t></span>`;
     }
     class Parent extends Component {
-      static template = xml`<Child flag="state.flag"/>`
+      static template = xml`<Child flag="state.flag"/>`;
       static components = { Child };
       state = useState({ flag: false });
     }