Respect calendarDelegate in showDateRangePicker (#168290)

This PR fixes an issue where the `calendarDelegate` parameter was not
respected by `showDateRangePicker`. Although support
for`calendarDelegate` was added in [PR
#161874](https://github.com/flutter/flutter/pull/161874), it was
inadvertently omitted from `showDateRangePicker`, causing
inconsistencies in behavior compared to `showDatePicker`.

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

packages/flutter/lib/src/material/date_picker.dart

@@ -1259,6 +1259,7 @@ Future<DateTimeRange?> showDateRangePicker({
     keyboardType: keyboardType,
     switchToInputEntryModeIcon: switchToInputEntryModeIcon,
     switchToCalendarEntryModeIcon: switchToCalendarEntryModeIcon,
+    calendarDelegate: calendarDelegate,
   );
 
   if (textDirection != null) {

packages/flutter/test/material/date_range_picker_test.dart

@@ -61,6 +61,7 @@ void main() {
     TextDirection textDirection = TextDirection.ltr,
     bool useMaterial3 = false,
     SelectableDayForRangePredicate? selectableDayPredicate,
+    CalendarDelegate<DateTime> calendarDelegate = const GregorianCalendarDelegate(),
   }) async {
     late BuildContext buttonContext;
     await tester.pumpWidget(
@@ -106,6 +107,7 @@ void main() {
       builder: (BuildContext context, Widget? child) {
         return Directionality(textDirection: textDirection, child: child ?? const SizedBox());
       },
+      calendarDelegate: calendarDelegate,
     );
 
     await tester.pumpAndSettle(const Duration(seconds: 1));
@@ -1868,6 +1870,49 @@ void main() {
       expect(dialog.calendarDelegate, isA<TestCalendarDelegate>());
     });
 
+    testWidgets('showDateRangePicker uses gregorian calendar delegate by default', (
+      WidgetTester tester,
+    ) async {
+      await preparePicker(tester, (Future<DateTimeRange?> range) async {
+        final Finder helpText = find.text('Select range');
+        final Finder firstDateHeaderText = find.text('Jan 15');
+        final Finder lastDateHeaderText = find.text('Jan 25, 2016');
+        final Finder saveText = find.text('Save');
+
+        expect(helpText, findsOneWidget);
+        expect(firstDateHeaderText, findsOneWidget);
+        expect(lastDateHeaderText, findsOneWidget);
+        expect(saveText, findsOneWidget);
+
+        final DateRangePickerDialog dialog = tester.widget(find.byType(DateRangePickerDialog));
+        expect(dialog.calendarDelegate, isA<GregorianCalendarDelegate>());
+      }, useMaterial3: true);
+    });
+
+    testWidgets('showDateRangePicker using custom calendar delegate implementation', (
+      WidgetTester tester,
+    ) async {
+      await preparePicker(
+        tester,
+        (Future<DateTimeRange?> range) async {
+          final Finder helpText = find.text('Select range');
+          final Finder firstDateHeaderText = find.text('Jan 15');
+          final Finder lastDateHeaderText = find.text('Jan 25, 2016');
+          final Finder saveText = find.text('Save');
+
+          expect(helpText, findsOneWidget);
+          expect(firstDateHeaderText, findsOneWidget);
+          expect(lastDateHeaderText, findsOneWidget);
+          expect(saveText, findsOneWidget);
+
+          final DateRangePickerDialog dialog = tester.widget(find.byType(DateRangePickerDialog));
+          expect(dialog.calendarDelegate, isA<TestCalendarDelegate>());
+        },
+        useMaterial3: true,
+        calendarDelegate: const TestCalendarDelegate(),
+      );
+    });
+
     testWidgets('Displays calendar based on the calendar delegate', (WidgetTester tester) async {
       Finder getMonthItem() {
         final Finder dayItem = find.descendant(