[go_router] Update generated output format (flutter#9817)

The Dart 3.7+ formatter does not remove all blank lines in function calls split across multile lines, so the generated+formatted output no longer matched expetations once the example app was changed to use a minimum SDK of 3.7. This updates the example app's min SDK (thus updating the autoformatting of all of its code), and changes the code generator such that running the new formatter on the output has the same results as it did with the previous formatter.
    
Unblocks flutter#9816

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Author: stuartmorgan-g

packages/go_router_builder/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.2.1
+
+- Changes generated whitespace for better compatibility with new Dart formatter.
+
 ## 3.2.0
 
 - Adds support for`extension type`.

packages/go_router_builder/README.md

@@ -103,9 +103,7 @@ The tree of routes is defined as an attribute on each of the top-level routes:
 @TypedGoRoute<HomeRoute>(
   path: '/',
   routes: <TypedGoRoute<GoRouteData>>[
-    TypedGoRoute<FamilyRoute>(
-      path: 'family/:fid',
-    ),
+    TypedGoRoute<FamilyRoute>(path: 'family/:fid'),
   ],
 )
 class HomeRoute extends GoRouteData with _$HomeRoute {
@@ -200,8 +198,9 @@ a return value. The generated routes also follow this functionality.
 
 <?code-excerpt "example/lib/readme_excerpts.dart (awaitPush)"?>
 ```dart
-final bool? result =
-    await const FamilyRoute(fid: 'John').push<bool>(context);
+final bool? result = await const FamilyRoute(
+  fid: 'John',
+).push<bool>(context);
 ```
 
 ## Query parameters
@@ -376,10 +375,7 @@ class MyMaterialRouteWithKey extends GoRouteData with _$MyMaterialRouteWithKey {
   static const LocalKey _key = ValueKey<String>('my-route-with-key');
   @override
   MaterialPage<void> buildPage(BuildContext context, GoRouterState state) {
-    return const MaterialPage<void>(
-      key: _key,
-      child: MyPage(),
-    );
+    return const MaterialPage<void>(key: _key, child: MyPage());
   }
 }
 ```
@@ -398,12 +394,17 @@ class FancyRoute extends GoRouteData with _$FancyRoute {
     GoRouterState state,
   ) {
     return CustomTransitionPage<void>(
-        key: state.pageKey,
-        child: const MyPage(),
-        transitionsBuilder: (BuildContext context, Animation<double> animation,
-            Animation<double> secondaryAnimation, Widget child) {
-          return RotationTransition(turns: animation, child: child);
-        });
+      key: state.pageKey,
+      child: const MyPage(),
+      transitionsBuilder: (
+        BuildContext context,
+        Animation<double> animation,
+        Animation<double> secondaryAnimation,
+        Widget child,
+      ) {
+        return RotationTransition(turns: animation, child: child);
+      },
+    );
   }
 }
 ```
@@ -449,6 +450,7 @@ class MyGoRouteData extends GoRouteData with _$MyGoRouteData {
   @override
   Widget build(BuildContext context, GoRouterState state) => const MyPage();
 }
+
 ```
 
 An example is available [here](https://github.com/flutter/packages/blob/main/packages/go_router_builder/example/lib/shell_route_with_keys_example.dart).