[IMP] reactivity: new primitives for reactivity

fine grained reactivity:

existing key in source changes --> only observer having read the key are notified

add/delete key in source changes --> all source observers are notified

Co-authored-by: Aaron Bohy <aab@odoo.com>
Co-authored-by: Géry Debongnie <ged@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>

tests/components/lifecycle.test.ts

@@ -493,7 +493,7 @@ describe("lifecycle hooks", () => {
     let n = 0;
 
     class Test extends Component {
-      static template = xml`<div/>`;
+      static template = xml`<div><t t-esc="state.a"/></div>`;
       state = useState({ a: 1 });
 
       setup() {