Replace the webviewx package with webview_flutter_web.

[timbotimbo]

Description

This replaces the webviewx package with webview_flutter_web. These are only used on the web platform.

The webviewx package relies on webview_flutter: ^2.0.13, which is currently at 4.0.2. This causes issues when a different webview is used in an app using a UnityWidget. #738

A workaround was to use dependency overrides in pubspec.yaml.

dependency_overrides:
  webview_flutter: [VERSION_YOU_NEED]

A recent webview_flutter_web update (0.2.2) makes it compatible with the Unity export.
To make things future-proof, let's change this to a webview that isn't abandoned.

Testing

The example project seems to work as expected.
I'd love feedback from anyone using Unity in a web project to see how this performs.

@Ahmadre Given that you added web, maybe you can take a look.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[drsmile1001]

How to help merge this?

[RoyalCoder88]

tested, everything is fine and passed all the tests