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/N8nUserSelect/UserSelect.vue

@@ -69,8 +69,8 @@ export default mixins(Locale).extend({
 	},
 	computed: {
 		fitleredUsers(): IUser[] {
-			return this.users
-				.filter((user: IUser) => {
+			return (this.users as IUser[])
+				.filter((user) => {
 					if (user.isPendingUser || !user.email) {
 						return false;
 					}
@@ -98,6 +98,10 @@ export default mixins(Locale).extend({
 					return a.firstName > b.firstName? 1 : -1;
 				}
 
+				if (!a.email || !b.email) {
+					throw new Error('Expected all users to have email');
+				}
+
 				return a.email > b.email ? 1 : -1;
 			});
 		},