Fix RawScrollbar examples and desktop test (#158237)

## Description

Fix the formatting of some `RawScrollbar` examples.
Fix and rename one test file (name without `_test` suffix).

dev/bots/check_code_samples.dart

@@ -312,5 +312,4 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/color_scheme/dynamic_content_color.0_test.dart',
   'examples/api/test/widgets/image/image.frame_builder.0_test.dart',
   'examples/api/test/widgets/image/image.loading_builder.0_test.dart',
-  'examples/api/test/widgets/scrollbar/raw_scrollbar.desktop.0_test.dart',
 };

examples/api/lib/widgets/scrollbar/raw_scrollbar.0.dart

@@ -32,11 +32,11 @@ class RawScrollbarExample extends StatefulWidget {
 }
 
 class _RawScrollbarExampleState extends State<RawScrollbarExample> {
-  final ScrollController _firstController = ScrollController();
+  final ScrollController _controller = ScrollController();
 
   @override
   void dispose() {
-    _firstController.dispose();
+    _controller.dispose();
     super.dispose();
   }
 
@@ -54,17 +54,19 @@ class _RawScrollbarExampleState extends State<RawScrollbarExample> {
             // from attaching to the PrimaryScrollController.
             child: Scrollbar(
               thumbVisibility: true,
-                controller: _firstController,
+              controller: _controller,
               child: ListView.builder(
-                    controller: _firstController,
+                controller: _controller,
                 itemCount: 100,
                 itemBuilder: (BuildContext context, int index) {
                   return Padding(
                     padding: const EdgeInsets.all(8.0),
                     child: Text('Scrollable 1 : Index $index'),
                   );
-                    }),
+                },
-              )),
+              ),
+            ),
+          ),
           SizedBox(
             width: constraints.maxWidth / 2,
             // This vertical scroll view has primary set to true, so it is
@@ -84,9 +86,12 @@ class _RawScrollbarExampleState extends State<RawScrollbarExample> {
                     child: Padding(
                       padding: const EdgeInsets.all(8.0),
                       child: Text('Scrollable 2 : Index $index'),
-                          ));
+                    ),
-                    }),
+                  );
-              )),
+                },
+              ),
+            ),
+          ),
         ],
       );
     });

examples/api/lib/widgets/scrollbar/raw_scrollbar.2.dart

@@ -30,21 +30,21 @@ class RawScrollbarExample extends StatefulWidget {
 }
 
 class _RawScrollbarExampleState extends State<RawScrollbarExample> {
-  final ScrollController _controllerOne = ScrollController();
+  final ScrollController _controller = ScrollController();
 
   @override
   void dispose() {
-    _controllerOne.dispose();
+    _controller.dispose();
     super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
     return RawScrollbar(
-      controller: _controllerOne,
+      controller: _controller,
       thumbVisibility: true,
       child: GridView.builder(
-        controller: _controllerOne,
+        controller: _controller,
         itemCount: 120,
         gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3),
         itemBuilder: (BuildContext context, int index) {

examples/api/lib/widgets/scrollbar/raw_scrollbar.desktop.0.dart

@@ -32,11 +32,11 @@ class DesktopExample extends StatefulWidget {
 }
 
 class _DesktopExampleState extends State<DesktopExample> {
-  final ScrollController controller = ScrollController();
+  final ScrollController _controller = ScrollController();
 
   @override
   void dispose() {
-    controller.dispose();
+    _controller.dispose();
     super.dispose();
   }
 
@@ -53,9 +53,9 @@ class _DesktopExampleState extends State<DesktopExample> {
             child: Scrollbar(
               thickness: 20.0,
               thumbVisibility: true,
-                controller: controller,
+              controller: _controller,
               child: ListView.builder(
-                  controller: controller,
+                controller: _controller,
                 itemCount: 100,
                 itemBuilder: (BuildContext context, int index) {
                   return SizedBox(
@@ -67,7 +67,8 @@ class _DesktopExampleState extends State<DesktopExample> {
                   );
                 },
               ),
-              )),
+            ),
+          ),
           SizedBox(
             width: constraints.maxWidth / 2,
             // When running this sample on desktop, one scrollbar will be
@@ -93,7 +94,8 @@ class _DesktopExampleState extends State<DesktopExample> {
                   },
                 ),
               ),
-              )),
+            ),
+          ),
         ],
       );
     });

examples/api/test/widgets/scrollbar/raw_scrollbar.desktop.0_test.dart

@@ -8,7 +8,6 @@ import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   testWidgets('Can hide default scrollbar on desktop', (WidgetTester tester) async {
-
     await tester.pumpWidget(
       const example.ScrollbarApp(),
     );
@@ -16,5 +15,5 @@ void main() {
     // Two from left list view where scroll configuration is not set.
     // One from right list view where scroll configuration is set.
     expect(find.byType(Scrollbar), findsNWidgets(3));
-  });
+  }, variant: TargetPlatformVariant.desktop());
 }