WASM Support

[lorisgir]

Describe the bug
I'm trying to run the unity player on flutter web with wasm enabled, but it gives me this error:
TargetPlatform.macOS is not yer supported by the unity player plugin.

I'm running this from my macbook pro. Is this an expected behaviour?

To Reproduce
Steps to reproduce the behavior:

1. Run on flutter web with --wasm

Expected behavior
The player running.

Unity (please complete the following information):

• OS: MacOS 14.6
• Version Unity 2022.3.43f1

Smartphone (please complete the following information):

• Device: Chrome

[lorisgir]

I tried to run the same code but switching to a windows pc and I got the same error:
TargetPlatform.windows is not yer supported by the unity player plugin.

[timbotimbo]

Looks like this conditional breaks as dart.library.html is not available with WASM.

flutter-unity-view-widget/lib/flutter_unity_widget.dart

Lines 4 to 6 in f51fedc

	export 'src/facade_widget.dart'
	if (dart.library.io) 'src/io/unity_widget.dart'
	if (dart.library.html) 'src/web/unity_widget.dart';

Dart:html is used plenty in web_unity_widget_controller.dart, so this plugin will need the dart:html to package:web migration to work on WASM.