🩹(react) harmonize date picker components output

By introducing this utility function, we ensure that any output value
is converted back to an ISO 8601 date and time string in UTC timezone.
Overall, it harmonize and factorize the way we output
values from date picker components.

packages/react/src/components/Forms/DatePicker/DatePicker.spec.tsx

@@ -1,16 +1,24 @@
 import userEvent from "@testing-library/user-event";
 import { render, screen, within } from "@testing-library/react";
 import React, { FormEvent, useState } from "react";
-import { afterEach, expect, vi } from "vitest";
+import { expect, vi } from "vitest";
 import { CunninghamProvider } from ":/components/Provider";
 import { DatePicker } from ":/components/Forms/DatePicker/DatePicker";
 import { Button } from ":/components/Button";
 
-describe("<DatePicker/>", () => {
-  afterEach(() => {
-    vi.restoreAllMocks();
-  });
+vi.mock("@internationalized/date", async () => {
+  const mod = await vi.importActual<typeof import("@internationalized/date")>(
+    "@internationalized/date"
+  );
+  return {
+    ...mod,
+    // Note: Restoring mocks will cause the function to return 'undefined'.
+    // Consider providing a default implementation to be restored instead.
+    getLocalTimeZone: vi.fn().mockReturnValue("Europe/Paris"),
+  };
+});
 
+describe("<DatePicker/>", () => {
   const expectCalendarToBeClosed = () => {
     expect(screen.queryByRole("application")).toBeNull();
   };
@@ -525,7 +533,7 @@ describe("<DatePicker/>", () => {
     expectCalendarToBeClosed();
 
     // Make sure value is selected.
-    screen.getByText(`Value = 2023-04-12|`);
+    screen.getByText(`Value = 2023-04-11T22:00:00.000Z|`);
 
     // Clear value.
     const clearButton = screen.getByRole("button", {
@@ -633,7 +641,7 @@ describe("<DatePicker/>", () => {
     expect(monthSegment).toHaveFocus();
 
     // Type date's value.
-    await user.keyboard("{1}{2}{5}{2}{0}{2}{3}");
+    await user.keyboard("{5}{1}{2}{2}{0}{2}{3}");
 
     // Submit form being filled with a date.
     await user.click(submitButton);
@@ -642,7 +650,7 @@ describe("<DatePicker/>", () => {
 
     // Make sure form's value matches.
     expect(formData).toEqual({
-      datepicker: "2023-12-05",
+      datepicker: "2023-05-11T22:00:00.000Z",
     });
 
     // Clear picked date.