Adding ScrollController support for Stepper widget (#128814)

This PR is to add **controller** property to the **Stepper** widget, so
that user has the flexibility to control the scroll offset for various
purposes(especially in case of scroll animations)!

Fixes #61207 

Co-authored-by: Taha Tesser <tessertaha@gmail.com>

Author: SwaroopSambhayya

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

@@ -202,6 +202,7 @@ class Stepper extends StatefulWidget {
   const Stepper({
     super.key,
     required this.steps,
+    this.controller,
     this.physics,
     this.type = StepperType.vertical,
     this.currentStep = 0,
@@ -230,6 +231,13 @@ class Stepper extends StatefulWidget {
   /// can be helpful to set this property to [ClampingScrollPhysics].
   final ScrollPhysics? physics;
 
+  /// An object that can be used to control the position to which this scroll
+  /// view is scrolled.
+  ///
+  /// To control the initial scroll offset of the scroll view, provide a
+  /// [controller] with its [ScrollController.initialScrollOffset] property set.
+  final ScrollController? controller;
+
   /// The type of stepper that determines the layout. In the case of
   /// [StepperType.horizontal], the content of the current step is displayed
   /// underneath as opposed to the [StepperType.vertical] case where it is
@@ -765,6 +773,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
 
   Widget _buildVertical() {
     return ListView(
+      controller: widget.controller,
       shrinkWrap: true,
       physics: widget.physics,
       children: <Widget>[
@@ -858,6 +867,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
         ),
         Expanded(
           child: ListView(
+            controller: widget.controller,
             physics: widget.physics,
             padding: const EdgeInsets.all(24.0),
             children: <Widget>[

packages/flutter/test/material/stepper_test.dart

@@ -972,6 +972,37 @@ testWidgets('Stepper custom indexed controls test', (WidgetTester tester) async
     }
   });
 
+  testWidgets('ScrollController is passed to the stepper listview', (WidgetTester tester) async {
+      final ScrollController controller = ScrollController();
+      for (final StepperType type in StepperType.values) {
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Material(
+              child: Stepper(
+                controller: controller,
+                type: type,
+                steps: const <Step>[
+                  Step(
+                    title: Text('Step 1'),
+                    content: SizedBox(
+                      width: 100.0,
+                      height: 100.0,
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        );
+
+        final ListView listView = tester.widget<ListView>(
+          find.descendant(of: find.byType(Stepper),
+          matching: find.byType(ListView),
+        ));
+        expect(listView.controller, controller);
+      }
+    });
+
   testWidgets('Stepper horizontal size test', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/pull/77732
     Widget buildFrame({ bool isActive = true, Brightness? brightness }) {