🩹(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/utils.spec.ts

@@ -1,5 +1,12 @@
-import { CalendarDate, DateValue, parseDate } from "@internationalized/date";
 import {
+  CalendarDate,
+  DateValue,
+  parseAbsolute,
+  parseDate,
+} from "@internationalized/date";
+import { vi } from "vitest";
+import {
+  convertDateValueToString,
   parseCalendarDate,
   parseRangeCalendarDate,
 } from ":/components/Forms/DatePicker/utils";
@@ -17,6 +24,18 @@ const expectDateToBeEqual = (
   expect(parsedDate?.day === expectedDay);
 };
 
+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("parseCalendarDate", () => {
   it.each([
     [2023, 4, 12],
@@ -161,3 +180,24 @@ describe("parseRangeCalendarDate", () => {
     expectDateToBeEqual(range?.end, 2023, 4, 22);
   });
 });
+
+describe("convertDateValueToString", () => {
+  it("should return an empty string for null date", () => {
+    const date: DateValue | null = null;
+    const result = convertDateValueToString(date);
+    expect(result).toBe("");
+  });
+
+  it("should return a UTC ISO 8601 string from a CalendarDate", async () => {
+    const date = parseDate("2023-05-25");
+    const result = convertDateValueToString(date);
+    expect(result).eq("2023-05-24T22:00:00.000Z");
+  });
+
+  it("should return a UTC ISO 8601 string from a ZonedDateTime", async () => {
+    // Europe/Paris is the mocked local timezone.
+    const date = parseAbsolute("2023-05-25T00:00:00.000+02:00", "Europe/Paris");
+    const result = convertDateValueToString(date);
+    expect(result).eq("2023-05-24T22:00:00.000Z");
+  });
+});