Add link to more detailed multidex information. (#104558)

Author: GaryQian

packages/flutter_tools/lib/src/android/gradle_errors.dart

@@ -101,6 +101,7 @@ final GradleHandledError multidexErrorHandler = GradleHandledError(
     if (multidexEnabled) {
       globals.printStatus(
         'Multidex support is required for your android app to build since the number of methods has exceeded 64k. '
+        'See https://docs.flutter.dev/deployment/android#enabling-multidex-support for more information. '
         "You may pass the --no-multidex flag to skip Flutter's multidex support to use a manual solution.\n",
         indent: 4,
       );

packages/flutter_tools/test/general.shard/android/gradle_errors_test.dart

@@ -361,6 +361,11 @@ Execution failed for task ':app:mergeDexDebug'.
           'Multidex support is required for your android app to build since the number of methods has exceeded 64k.'
         )
       );
+      expect(testLogger.statusText,
+        contains(
+          'See https://docs.flutter.dev/deployment/android#enabling-multidex-support for more information.'
+        )
+      );
       expect(testLogger.statusText,
         contains(
           'Your `android/app/src/main/AndroidManifest.xml` does not contain'