Fix all type errors in design system (#3956)

* 📘 Fix type errors in design system

* 🔥 Remove unneeded `?`

* 🔧 Add design system to Vetur

* 📘 Improve typing of `$el`

* ♻️ Address feedback

* 📘 Type leftover `MouseEvent`

* 📘 Type `event.target` properly

packages/design-system/src/components/N8nCheckbox/Checkbox.vue

@@ -56,8 +56,8 @@ export default Vue.extend({
 		},
 	},
 	methods: {
-		onChange(e) {
-			this.$emit("input", e);
+		onChange(event: Event) {
+			this.$emit("input", event);
 		},
 	}
 });