Use utf8.encode() instead of longer const Utf8Encoder.convert() (#130567)

The change in [0] has propagated now everywhere, so we can use
`utf8.encode()` instead of the longer `const Utf8Encoder.convert()`.

Also it cleans up code like

```
  TypedData bytes;
  bytes.buffer.asByteData();
```

as that is not guaranteed to be correct, the correct version would be

```
  TypedData bytes;
  bytes.buffer.asByteData(bytes.offsetInBytes, bytes.lengthInBytes);
```

a shorter hand for that is:

```
  TypedData bytes;
  ByteData.sublistView(bytes);
```

[0] https://github.com/dart-lang/sdk/issues/52801

packages/flutter/lib/src/services/asset_bundle.dart

@@ -57,11 +57,10 @@ abstract class AssetBundle {
   /// Throws an exception if the asset is not found.
   ///
   /// The returned [ByteData] can be converted to a [Uint8List] (a list of bytes)
-  /// using [ByteData.buffer] to obtain a [ByteBuffer], and then
-  /// [ByteBuffer.asUint8List] to obtain the byte list. Lists of bytes can be
-  /// used with APIs that accept [Uint8List] objects, such as
-  /// [decodeImageFromList], as well as any API that accepts a [List<int>], such
-  /// as [File.writeAsBytes] or [Utf8Codec.decode] (accessible via [utf8]).
+  /// using [Uint8List.sublistView]. Lists of bytes can be used with APIs that
+  /// accept [Uint8List] objects, such as [decodeImageFromList], as well as any
+  /// API that accepts a [List<int>], such as [File.writeAsBytes] or
+  /// [Utf8Codec.decode] (accessible via [utf8]).
   Future<ByteData> load(String key);
 
   /// Retrieve a binary resource from the asset bundle as an immutable
@@ -70,7 +69,7 @@ abstract class AssetBundle {
   /// Throws an exception if the asset is not found.
   Future<ui.ImmutableBuffer> loadBuffer(String key) async {
     final ByteData data = await load(key);
-    return ui.ImmutableBuffer.fromUint8List(data.buffer.asUint8List());
+    return ui.ImmutableBuffer.fromUint8List(Uint8List.sublistView(data));
   }
 
   /// Retrieve a string from the asset bundle.
@@ -91,7 +90,7 @@ abstract class AssetBundle {
     // 50 KB of data should take 2-3 ms to parse on a Moto G4, and about 400 μs
     // on a Pixel 4.
     if (data.lengthInBytes < 50 * 1024) {
-      return utf8.decode(data.buffer.asUint8List());
+      return utf8.decode(Uint8List.sublistView(data));
     }
     // For strings larger than 50 KB, run the computation in an isolate to
     // avoid causing main thread jank.
@@ -99,7 +98,7 @@ abstract class AssetBundle {
   }
 
   static String _utf8decode(ByteData data) {
-    return utf8.decode(data.buffer.asUint8List());
+    return utf8.decode(Uint8List.sublistView(data));
   }
 
   /// Retrieve a string from the asset bundle, parse it with the given function,
@@ -161,7 +160,7 @@ class NetworkAssetBundle extends AssetBundle {
       ]);
     }
     final Uint8List bytes = await consolidateHttpClientResponseBytes(response);
-    return bytes.buffer.asByteData();
+    return ByteData.sublistView(bytes);
   }
 
   // TODO(ianh): Once the underlying network logic learns about caching, we
@@ -308,7 +307,7 @@ abstract class CachingAssetBundle extends AssetBundle {
   @override
   Future<ui.ImmutableBuffer> loadBuffer(String key) async {
     final ByteData data = await load(key);
-    return ui.ImmutableBuffer.fromUint8List(data.buffer.asUint8List());
+    return ui.ImmutableBuffer.fromUint8List(Uint8List.sublistView(data));
   }
 }
 
@@ -316,10 +315,10 @@ abstract class CachingAssetBundle extends AssetBundle {
 class PlatformAssetBundle extends CachingAssetBundle {
   @override
   Future<ByteData> load(String key) {
-    final Uint8List encoded = utf8.encoder.convert(Uri(path: Uri.encodeFull(key)).path);
+    final Uint8List encoded = utf8.encode(Uri(path: Uri.encodeFull(key)).path);
     final Future<ByteData>? future = ServicesBinding.instance.defaultBinaryMessenger.send(
       'flutter/assets',
-      encoded.buffer.asByteData(),
+      ByteData.sublistView(encoded),
     )?.then((ByteData? asset) {
       if (asset == null) {
         throw FlutterError.fromParts(<DiagnosticsNode>[
@@ -342,7 +341,7 @@ class PlatformAssetBundle extends CachingAssetBundle {
   Future<ui.ImmutableBuffer> loadBuffer(String key) async {
     if (kIsWeb) {
       final ByteData bytes = await load(key);
-      return ui.ImmutableBuffer.fromUint8List(bytes.buffer.asUint8List());
+      return ui.ImmutableBuffer.fromUint8List(Uint8List.sublistView(bytes));
     }
     bool debugUsePlatformChannel = false;
     assert(() {
@@ -358,7 +357,7 @@ class PlatformAssetBundle extends CachingAssetBundle {
     }());
     if (debugUsePlatformChannel) {
       final ByteData bytes = await load(key);
-      return ui.ImmutableBuffer.fromUint8List(bytes.buffer.asUint8List());
+      return ui.ImmutableBuffer.fromUint8List(Uint8List.sublistView(bytes));
     }
     try {
       return await ui.ImmutableBuffer.fromAsset(key);

packages/flutter/lib/src/services/message_codecs.dart

@@ -50,7 +50,7 @@ class StringCodec implements MessageCodec<String> {
     if (message == null) {
       return null;
     }
-    return utf8.decoder.convert(message.buffer.asUint8List(message.offsetInBytes, message.lengthInBytes));
+    return utf8.decode(Uint8List.sublistView(message));
   }
 
   @override
@@ -58,8 +58,7 @@ class StringCodec implements MessageCodec<String> {
     if (message == null) {
       return null;
     }
-    final Uint8List encoded = utf8.encoder.convert(message);
-    return encoded.buffer.asByteData();
+    return ByteData.sublistView(utf8.encode(message));
   }
 }
 
@@ -415,7 +414,7 @@ class StandardMessageCodec implements MessageCodec<Object?> {
         if (char <= 0x7f) {
           asciiBytes[i] = char;
         } else {
-          utf8Bytes = utf8.encoder.convert(value.substring(i));
+          utf8Bytes = utf8.encode(value.substring(i));
           utf8Offset = i;
           break;
         }

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

@@ -6176,7 +6176,7 @@ class RawImage extends LeafRenderObjectWidget {
 ///   @override
 ///   Future<ByteData> load(String key) async {
 ///     if (key == 'resources/test') {
-///       return ByteData.view(Uint8List.fromList(utf8.encode('Hello World!')).buffer);
+///       return ByteData.sublistView(utf8.encode('Hello World!'));
 ///     }
 ///     return ByteData(0);
 ///   }

packages/flutter/test/services/asset_bundle_test.dart

@@ -16,17 +16,16 @@ class TestAssetBundle extends CachingAssetBundle {
   Future<ByteData> load(String key) async {
     loadCallCount[key] = (loadCallCount[key] ?? 0) + 1;
     if (key == 'AssetManifest.json') {
-      return ByteData.view(Uint8List.fromList(const Utf8Encoder().convert('{"one": ["one"]}')).buffer);
+      return ByteData.sublistView(utf8.encode('{"one": ["one"]}'));
     }
 
     if (key == 'AssetManifest.bin') {
-      return const StandardMessageCodec().encodeMessage(<String, Object>{
-        'one': <Object>[]
-      })!;
+      return const StandardMessageCodec()
+          .encodeMessage(<String, Object>{'one': <Object>[]})!;
     }
 
     if (key == 'counter') {
-      return ByteData.view(Uint8List.fromList(const Utf8Encoder().convert(loadCallCount[key]!.toString())).buffer);
+      return ByteData.sublistView(utf8.encode(loadCallCount[key]!.toString()));
     }
 
     if (key == 'one') {

packages/flutter/test/services/binding_test.dart

@@ -89,7 +89,7 @@ void main() {
     int flutterAssetsCallCount = 0;
     binding.defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) async {
       flutterAssetsCallCount += 1;
-      return Uint8List.fromList('test_asset_data'.codeUnits).buffer.asByteData();
+      return ByteData.sublistView(utf8.encode('test_asset_data'));
     });
 
     await rootBundle.loadString('test_asset');

packages/flutter/test/services/channel_buffers_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:convert';
-import 'dart:typed_data';
 import 'dart:ui' as ui;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
@@ -14,15 +13,11 @@ class TestChannelBuffersFlutterBinding extends BindingBase with SchedulerBinding
 
 void main() {
   ByteData makeByteData(String str) {
-    final List<int> list = utf8.encode(str);
-    final ByteBuffer buffer = list is Uint8List ? list.buffer : Uint8List.fromList(list).buffer;
-    return ByteData.view(buffer);
+    return ByteData.sublistView(utf8.encode(str));
   }
 
   String getString(ByteData data) {
-    final ByteBuffer buffer = data.buffer;
-    final List<int> list = buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
-    return utf8.decode(list);
+    return utf8.decode(Uint8List.sublistView(data));
   }
 
   test('does drain channel buffers', () async {

packages/flutter/test/services/default_binary_messenger_test.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:typed_data';
 
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -13,10 +12,7 @@ void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
   ByteData makeByteData(String str) {
-    final List<int> list = utf8.encode(str);
-    final ByteBuffer buffer =
-        list is Uint8List ? list.buffer : Uint8List.fromList(list).buffer;
-    return ByteData.view(buffer);
+    return ByteData.sublistView(utf8.encode(str));
   }
 
   test('default binary messenger calls callback once', () async {