fix: Add conditional export to support --wasm build (#3363)

* fix: Add conditional export to support --wasm build

* Add stubs for extension

---------

Co-authored-by: Simon Binder <oss@simonbinder.eu>

drift/lib/src/web/channel_legacy_dummy.dart

@@ -0,0 +1,27 @@
+import 'package:stream_channel/stream_channel.dart';
+
+/// Extension to transform a raw `MessagePort` from web workers into a Dart
+/// [StreamChannel].
+extension PortToChannel on dynamic {
+  /// Converts this port to a two-way communication channel, exposed as a
+  /// [StreamChannel].
+  ///
+  /// This can be used to implement a remote database connection over service
+  /// workers.
+  ///
+  /// The [explicitClose] parameter can be used to control whether a close
+  /// message should be sent through the channel when it is closed. This will
+  /// cause it to be closed on the other end as well. Note that this is not a
+  /// reliable way of determining channel closures though, as there is no event
+  /// for channels being closed due to a tab or worker being closed.
+  /// Both "ends" of a JS channel calling [channel] on their part must use the
+  /// value for [explicitClose].
+  @Deprecated(
+    'Please use MessagePorts from package:web instead of those from dart:html. '
+    'This extension will be removed from drift once `dart:html` is removed '
+    'from the SDK.',
+  )
+  StreamChannel<Object?> channel({bool explicitClose = false}) {
+    throw 'If this import was resolved, dart:html is not available.';
+  }
+}

drift/lib/web.dart

@@ -12,5 +12,6 @@ library drift.web;
 export 'src/web/sql_js.dart';
 export 'src/web/storage.dart' hide CustomSchemaVersionSave;
 export 'src/web/web_db.dart';
-export 'src/web/channel_legacy.dart';
+export 'src/web/channel_legacy_dummy.dart'
+    if (dart.library.html) 'src/web/channel_legacy.dart';
 export 'src/web/channel_new.dart';