Use utf8.encode() instead of longer const Utf8Encoder.convert() (flutter#43675)

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

```
  Uint8List bytes;
  bytes.buffer.asByteData();
```

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

```
  Uint8List bytes;
  bytes.buffer.asByteData(bytes.offsetInBytes, bytes.length);
```

a shorter hand for that is:

```
  Uint8List bytes;
  ByteData.sublistView(bytes);
```

[0] dart-lang/sdk#52801

Author: mkustermann

lib/ui/text.dart

@@ -3338,7 +3338,7 @@ Future<void> loadFontFromList(Uint8List list, {String? fontFamily}) {
   ).then((_) => _sendFontChangeMessage());
 }
 
-final ByteData _fontChangeMessage = utf8.encoder.convert(
+final ByteData _fontChangeMessage = utf8.encode(
   json.encode(<String, Object?>{'type': 'fontsChange'})
 ).buffer.asByteData();
 

lib/web_ui/lib/src/engine/platform_dispatcher.dart

@@ -1001,7 +1001,7 @@ class EnginePlatformDispatcher extends ui.PlatformDispatcher {
   void _setAppLifecycleState(ui.AppLifecycleState state) {
     sendPlatformMessage(
       'flutter/lifecycle',
-      Uint8List.fromList(utf8.encode(state.toString())).buffer.asByteData(),
+      ByteData.sublistView(utf8.encode(state.toString())),
       null,
     );
   }

lib/web_ui/lib/src/engine/services/message_codecs.dart

@@ -39,7 +39,7 @@ class StringCodec implements MessageCodec<String> {
 
   @override
   ByteData encodeMessage(String message) {
-    final Uint8List encoded = utf8.encoder.convert(message);
+    final Uint8List encoded = utf8.encode(message);
     return encoded.buffer.asByteData();
   }
 }
@@ -320,7 +320,7 @@ class StandardMessageCodec implements MessageCodec<dynamic> {
       }
     } else if (value is String) {
       buffer.putUint8(_valueString);
-      final List<int> bytes = utf8.encoder.convert(value);
+      final List<int> bytes = utf8.encode(value);
       writeSize(buffer, bytes.length);
       buffer.putUint8List(bytes as Uint8List);
     } else if (value is Uint8List) {

lib/web_ui/lib/src/engine/skwasm/skwasm_impl/raw/raw_memory.dart

@@ -26,8 +26,7 @@ external void stackRestore(StackPointer pointer);
 
 class StackScope {
   Pointer<Int8> convertStringToNative(String string) {
-    final Utf8Encoder utf8Encoder = utf8.encoder;
-    final Uint8List encoded = utf8Encoder.convert(string);
+    final Uint8List encoded = utf8.encode(string);
     final Pointer<Int8> pointer = allocInt8Array(encoded.length + 1);
     for (int i = 0; i < encoded.length; i++) {
       pointer[i] = encoded[i];

lib/web_ui/lib/ui_web/src/ui_web/asset_manager.dart

@@ -92,7 +92,7 @@ class AssetManager {
 
     if (response.status == 404 && asset == 'AssetManifest.json') {
       printWarning('Asset manifest does not exist at `$url` - ignoring.');
-      return Uint8List.fromList(utf8.encode('{}')).buffer.asByteData();
+      return ByteData.sublistView(utf8.encode('{}'));
     }
 
     return (await response.payload.asByteBuffer()).asByteData();

lib/web_ui/test/canvaskit/fragment_program_test.dart

@@ -186,7 +186,7 @@ void testMain() {
   });
 
   test('FragmentProgram can be created from JSON IPLR bundle', () {
-    final Uint8List data = const Utf8Encoder().convert(kJsonIPLR);
+    final Uint8List data = utf8.encode(kJsonIPLR);
     final CkFragmentProgram program = CkFragmentProgram.fromBytes('test', data);
 
     expect(program.effect, isNotNull);

lib/web_ui/test/common/fake_asset_manager.dart

@@ -90,7 +90,7 @@ class FakeAssetScope {
 FakeAssetManager fakeAssetManager = FakeAssetManager();
 
 ByteData stringAsUtf8Data(String string) {
-  return ByteData.view(Uint8List.fromList(utf8.encode(string)).buffer);
+  return ByteData.sublistView(utf8.encode(string));
 }
 
 const String ahemFontFamily = 'Ahem';

lib/web_ui/test/engine/channel_buffers_test.dart

@@ -23,7 +23,7 @@ void main() {
 }
 
 ByteData _makeByteData(String str) {
-  final Uint8List list = const Utf8Encoder().convert(str);
+  final Uint8List list = utf8.encode(str);
   final ByteBuffer buffer = list.buffer;
   return ByteData.view(buffer);
 }

lib/web_ui/test/ui/fragment_shader_test.dart

@@ -53,7 +53,7 @@ Future<void> testMain() async {
     assetScope = fakeAssetManager.pushAssetScope();
     assetScope.setAsset(
       'voronoi_shader',
-      Uint8List.fromList(utf8.encode(kVoronoiShaderSksl)).buffer.asByteData()
+      ByteData.sublistView(utf8.encode(kVoronoiShaderSksl))
     );
   });
 

lib/web_ui/test/ui/image_golden_test.dart

@@ -69,7 +69,7 @@ Future<void> testMain() async {
     assetScope = fakeAssetManager.pushAssetScope();
     assetScope.setAsset(
       'glitch_shader',
-      Uint8List.fromList(utf8.encode(kGlitchShaderSksl)).buffer.asByteData()
+      ByteData.sublistView(utf8.encode(kGlitchShaderSksl))
     );
   });