feat: add a deduplicate function

packages/ra-cubicweb/src/utils/__tests__/deduplicate.ts

+import { deduplicate } from "../deduplicate";
+
+describe("deduplicate", () => {
+  it('returns ["foo"] for ["foo", "foo"]', () => {
+    const deduplicated = deduplicate(["foo", "foo"]);
+
+    expect(deduplicated).toEqual(["foo"]);
+  });
+});

packages/ra-cubicweb/src/utils/deduplicate.ts

+export function deduplicate<E extends string>(array: E[]): E[] {
+  const deduplicated: E[] = [];
+  for (const element of array) {
+    if (!deduplicated.includes(element)) {
+      deduplicated.push(element);
+    }
+  }
+  return deduplicated;
+}