Wasm support

[rokk4]

Make flutter-stripe not hinder wasm compilation.

    Context: The unavailable library 'dart:html' is imported through these packages:
    
    web_plugin_registrant.dart => package:flutter_stripe_web => dart:html
    web_plugin_registrant.dart => package:flutter_stripe_web => package:stripe_js => dart:html

Describe the solution you'd like Move away from dart:html and dart:js

package:web, which replaces dart:html (and other web libraries) dart:js_interop, which replaces package:js and dart:js

https://docs.flutter.dev/platform-integration/web/wasm#js-interop-wasm