[flutter_svg] loader buffer fix (flutter#9898)

Fixes buffer access when loading svg from assets. Making it consistent with Image.asset loading. 

Basically changes: 
```String provideSvg(ByteData? message) => utf8.decode(message!.buffer.asUint8List(), allowMalformed: true);```
to:
```String provideSvg(ByteData? message) =>utf8.decode(Uint8List.sublistView(message!));```

since we do not want to decode whole buffer.
This is useful when using custom `AssetBundles`, like when they provide as slice of buffer on `load()` instead of allocating a new array of bytes.

Fixes flutter/flutter#174526

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Author: bshishov

third_party/packages/flutter_svg/CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 2.2.1
 
+* Fixes message buffer access in SvgAssetLoader.
 * Updates minimum supported SDK version to Flutter 3.29/Dart 3.7.
 
 ## 2.2.0

third_party/packages/flutter_svg/lib/src/loaders.dart

@@ -379,7 +379,7 @@ class SvgAssetLoader extends SvgLoader<ByteData> {
 
   @override
   String provideSvg(ByteData? message) =>
-      utf8.decode(message!.buffer.asUint8List(), allowMalformed: true);
+      utf8.decode(Uint8List.sublistView(message!), allowMalformed: true);
 
   @override
   SvgCacheKey cacheKey(BuildContext? context) {

third_party/packages/flutter_svg/pubspec.yaml

@@ -2,7 +2,7 @@ name: flutter_svg
 description: An SVG rendering and widget library for Flutter, which allows painting and displaying Scalable Vector Graphics 1.1 files.
 repository: https://github.com/flutter/packages/tree/main/third_party/packages/flutter_svg
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_svg%22
-version: 2.2.0
+version: 2.2.1
 
 environment:
   sdk: ^3.7.0

third_party/packages/flutter_svg/test/loaders_test.dart

@@ -1,3 +1,6 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_svg/flutter_svg.dart';
@@ -64,6 +67,29 @@ void main() {
     expect((await packageLoader.prepareMessage(null))!.lengthInBytes, 1);
   });
 
+  test('AssetLoader correctly accesses buffer', () async {
+    final ByteBuffer buffer = utf8.encode('foobar').buffer;
+    final TestBundle bundle = TestBundle(<String, ByteData>{
+      'foo': buffer.asByteData(0, 3),
+      'bar': buffer.asByteData(3, 3),
+    });
+    final SvgAssetLoader loaderFoo = SvgAssetLoader('foo', assetBundle: bundle);
+    final SvgAssetLoader loaderBar = SvgAssetLoader('bar', assetBundle: bundle);
+    final ByteData? byteDataFoo = await loaderFoo.prepareMessage(null);
+    final ByteData? byteDataBar = await loaderBar.prepareMessage(null);
+
+    expect(byteDataFoo!.buffer, equals(byteDataBar!.buffer));
+
+    expect(byteDataFoo.lengthInBytes, 3);
+    expect(byteDataFoo.offsetInBytes, 0);
+
+    expect(byteDataBar.offsetInBytes, 3);
+    expect(byteDataBar.lengthInBytes, 3);
+
+    expect(loaderFoo.provideSvg(byteDataFoo), equals('foo'));
+    expect(loaderBar.provideSvg(byteDataBar), equals('bar'));
+  });
+
   test('SvgNetworkLoader closes internal client', () async {
     final List<VerifyCloseClient> createdClients = <VerifyCloseClient>[];