Refactor refresh_indicator.1.dart to not use shrinkwrap (#129377)

This PR changes the example app into a custom scrollview with three slivers. The middle sliver has a nested scrollview of height 300 and only this nested sliver can trigger the refresh indicator.

Fixes https://github.com/flutter/flutter/issues/116237.

examples/api/lib/material/refresh_indicator/refresh_indicator.1.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 
 /// Flutter code sample for [RefreshIndicator].
@@ -13,8 +14,9 @@ class RefreshIndicatorExampleApp extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return const MaterialApp(
-      home: RefreshIndicatorExample(),
+    return MaterialApp(
+      scrollBehavior: const MaterialScrollBehavior().copyWith(dragDevices: PointerDeviceKind.values.toSet()),
+      home: const RefreshIndicatorExample(),
     );
   }
 }
@@ -40,17 +42,17 @@ class RefreshIndicatorExample extends StatelessWidget {
         // from the widget's children.
         //
         // By default this is set to `notification.depth == 0`, which ensures
-        // the only the scroll notifications from the first child are listened to.
+        // the only the scroll notifications from the first scroll view are listened to.
         //
         // Here setting `notification.depth == 1` triggers the refresh indicator
         // when overscrolling the nested scroll view.
         notificationPredicate: (ScrollNotification notification) {
           return notification.depth == 1;
         },
-        child: SingleChildScrollView(
-          child: Column(
-            children: <Widget>[
-              Container(
+        child: CustomScrollView(
+          slivers: <Widget>[
+            SliverToBoxAdapter(
+              child: Container(
                 height: 100,
                 alignment: Alignment.center,
                 color: Colors.pink[100],
@@ -65,10 +67,12 @@ class RefreshIndicatorExample extends StatelessWidget {
                   ],
                 ),
               ),
-              Container(
+            ),
+            SliverToBoxAdapter(
+              child: Container(
                 color: Colors.green[100],
+                height: 300,
                 child: ListView.builder(
-                  shrinkWrap: true,
                   itemCount: 25,
                   itemBuilder: (BuildContext context, int index) {
                     return const ListTile(
@@ -78,8 +82,17 @@ class RefreshIndicatorExample extends StatelessWidget {
                   },
                 ),
               ),
-            ],
-          ),
+            ),
+            SliverList.builder(
+              itemCount: 20,
+              itemBuilder: (BuildContext context, int index) {
+                return const ListTile(
+                  title: Text('Pull down here'),
+                  subtitle: Text("Refresh indicator won't trigger"),
+                );
+              }
+            )
+          ],
         ),
       ),
     );