Update navigationBar label's maxScaleFactor to meet GAR requirement (#141998)

fixes: https://github.com/flutter/flutter/issues/141997

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

@@ -18,6 +18,7 @@ import 'tooltip.dart';
 
 const double _kIndicatorHeight = 32;
 const double _kIndicatorWidth = 64;
+const double _kMaxLabelTextScaleFactor = 1.3;
 
 // Examples can assume:
 // late BuildContext context;
@@ -422,9 +423,11 @@ class NavigationDestination extends StatelessWidget {
         return Padding(
           padding: const EdgeInsets.only(top: 4),
           child: MediaQuery.withClampedTextScaling(
-            // Don't scale labels of destinations, instead, tooltip text will
-            // upscale.
-            maxScaleFactor: 1.0,
+            // Set maximum text scale factor to _kMaxLabelTextScaleFactor for the
+            // label to keep the visual hierarchy the same even with larger font
+            // sizes. To opt out, wrap the [label] widget in a [MediaQuery] widget
+            // with a different `TextScaler`.
+            maxScaleFactor: _kMaxLabelTextScaleFactor,
             child: Text(label, style: textStyle),
           ),
         );

packages/flutter/test/material/navigation_bar_test.dart

@@ -425,6 +425,71 @@ void main() {
     }
   });
 
+    testWidgets('Material3 - NavigationBar label can scale and has maxScaleFactor', (WidgetTester tester) async {
+    const String label = 'A';
+
+    Widget buildApp({ required TextScaler textScaler }) {
+      return MediaQuery(
+        data: MediaQueryData(textScaler: textScaler),
+        child: Localizations(
+          locale: const Locale('en', 'US'),
+          delegates: const <LocalizationsDelegate<dynamic>>[
+            DefaultMaterialLocalizations.delegate,
+            DefaultWidgetsLocalizations.delegate,
+          ],
+          child: MaterialApp(
+            home: Navigator(
+              onGenerateRoute: (RouteSettings settings) {
+                return MaterialPageRoute<void>(
+                  builder: (BuildContext context) {
+                    return Scaffold(
+                      bottomNavigationBar: NavigationBar(
+                        destinations: const <NavigationDestination>[
+                          NavigationDestination(
+                            label: label,
+                            icon: Icon(Icons.ac_unit),
+                          ),
+                          NavigationDestination(
+                            label: 'B',
+                            icon: Icon(Icons.battery_alert),
+                          ),
+                        ],
+                      ),
+                    );
+                  },
+                );
+              },
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: TextScaler.noScaling));
+    expect(find.text(label), findsOneWidget);
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect( _sizeAlmostEqual(tester.getSize(find.text(label)), const Size(12.5, 16.0)), true);
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(1.1)));
+    await tester.pumpAndSettle();
+
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect( _sizeAlmostEqual(tester.getSize(find.text(label)), const Size(13.7, 18.0)), true);
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(1.3)));
+
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect( _sizeAlmostEqual(tester.getSize(find.text(label)), const Size(16.1, 21.0)), true);
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(4)));
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect( _sizeAlmostEqual(tester.getSize(find.text(label)), const Size(16.1, 21.0)), true);
+    }
+  });
+
   testWidgets('Custom tooltips in NavigationBarDestination', (WidgetTester tester) async {
     await tester.pumpWidget(
       MaterialApp(
@@ -1499,3 +1564,8 @@ class IconWithRandomColor extends StatelessWidget {
     return Icon(icon, color: randomColor);
   }
 }
+
+
+bool _sizeAlmostEqual(Size a, Size b, {double maxDiff=0.05}) {
+  return (a.width - b.width).abs() <= maxDiff && (a.height - b.height).abs() <= maxDiff;
+}