[flutter_markdown] Support wasm (#6168)

Drop usage of dart:html

Author: kevmoo

packages/flutter_markdown/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.20+1
+
+* Updates minimum supported SDK version to Flutter 3.19.
+
 ## 0.6.20
 
 * Adds `textScaler` to `MarkdownStyleSheet`, and deprecates `textScaleFactor`.

packages/flutter_markdown/lib/src/_functions_web.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:html'; // ignore: avoid_web_libraries_in_flutter
+import 'dart:js_interop';
 
 import 'package:flutter/cupertino.dart' show CupertinoTheme;
 import 'package:flutter/material.dart' show Theme;
@@ -50,20 +50,14 @@ final MarkdownStyleSheet Function(BuildContext, MarkdownStyleSheetBaseTheme?)
   BuildContext context,
   MarkdownStyleSheetBaseTheme? baseTheme,
 ) {
-  MarkdownStyleSheet result;
-  switch (baseTheme) {
-    case MarkdownStyleSheetBaseTheme.platform:
-      final String userAgent = window.navigator.userAgent;
-      result = userAgent.contains('Mac OS X')
-          ? MarkdownStyleSheet.fromCupertinoTheme(CupertinoTheme.of(context))
-          : MarkdownStyleSheet.fromTheme(Theme.of(context));
-    case MarkdownStyleSheetBaseTheme.cupertino:
-      result =
-          MarkdownStyleSheet.fromCupertinoTheme(CupertinoTheme.of(context));
-    case MarkdownStyleSheetBaseTheme.material:
-    default: // ignore: no_default_cases
-      result = MarkdownStyleSheet.fromTheme(Theme.of(context));
-  }
+  final MarkdownStyleSheet result = switch (baseTheme) {
+    MarkdownStyleSheetBaseTheme.platform
+        when _userAgent.toDart.contains('Mac OS X') =>
+      MarkdownStyleSheet.fromCupertinoTheme(CupertinoTheme.of(context)),
+    MarkdownStyleSheetBaseTheme.cupertino =>
+      MarkdownStyleSheet.fromCupertinoTheme(CupertinoTheme.of(context)),
+    _ => MarkdownStyleSheet.fromTheme(Theme.of(context)),
+  };
 
   return result.copyWith(
     textScaler: MediaQuery.textScalerOf(context),
@@ -84,3 +78,6 @@ Widget _handleDataSchemeUri(
   }
   return const SizedBox();
 }
+
+@JS('window.navigator.userAgent')
+external JSString get _userAgent;

packages/flutter_markdown/lib/src/builder.dart

@@ -2,14 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// ignore: unnecessary_import, see https://github.com/flutter/flutter/pull/138881
-import 'dart:ui';
-
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:markdown/markdown.dart' as md;
 
-import '_functions_io.dart' if (dart.library.html) '_functions_web.dart';
+import '_functions_io.dart' if (dart.library.js_interop) '_functions_web.dart';
 import 'style_sheet.dart';
 import 'widget.dart';
 

packages/flutter_markdown/pubspec.yaml

@@ -4,11 +4,11 @@ description: A Markdown renderer for Flutter. Create rich text output,
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.6.20
+version: 0.6.20+1
 
 environment:
-  sdk: ^3.2.0
-  flutter: ">=3.16.0"
+  sdk: ^3.3.0
+  flutter: ">=3.19.0"
 
 dependencies:
   flutter: