Update image.error_builder.0.dart to replace the emoji with some text (flutter#176886)

fixes flutter#174805
after some investigation i found that `dart doc ` only understands
`utf-8 encoding` so providing an `emoji` for example breaks it(no crash
but not the intended behavior).

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---------

Co-authored-by: Victor Sanni <victorsanniay@gmail.com>

Author: AbdeMohlbi

examples/api/lib/widgets/image/image.error_builder.0.dart

@@ -39,7 +39,7 @@ class ErrorBuilderExample extends StatelessWidget {
           //   exception,
           //   stackTrace,
           // );
-          return const Text('😢');
+          return const Text('Image failed to load');
         },
       ),
     );

examples/api/test/widgets/image/image.error_builder.0_test.dart

@@ -25,7 +25,7 @@ void main() {
     expect(imageProvider.url, equals('https://example.does.not.exist/image.jpg'));
   });
 
-  testWidgets('errorBuilder returns text with emoji', (WidgetTester tester) async {
+  testWidgets('errorBuilder returns text', (WidgetTester tester) async {
     await tester.pumpWidget(const example.ErrorBuilderExampleApp());
     await tester.pumpAndSettle();
 
@@ -35,7 +35,7 @@ void main() {
 
     expect(
       errorBuilder(context, const HttpException('oops'), StackTrace.empty),
-      isA<Text>().having((Text text) => text.data, 'data', equals('😢')),
+      isA<Text>().having((Text text) => text.data, 'data', equals('Image failed to load')),
     );
   });
 }

packages/flutter/lib/src/widgets/image.dart

@@ -869,8 +869,9 @@ class Image extends StatefulWidget {
   /// the exception by providing a replacement widget, or rethrow the exception.
   ///
   /// {@tool dartpad}
-  /// The following sample uses [errorBuilder] to show a '😢' in place of the
-  /// image that fails to load, and prints the error to the console.
+  /// The following sample uses [errorBuilder] to show 'Image
+  /// failed to load' in place of the image that fails to load, and prints
+  /// the error to the console.
   ///
   /// ** See code in examples/api/lib/widgets/image/image.error_builder.0.dart **
   /// {@end-tool}