Always create a new track on web

[renefloor]

🎯 Goal

Fix screen sharing on web.
Fixes FLU-124

🛠 Implementation details

When starting to share your screen on web the _setTrackEnabled is called, but the deviceId is always null for the requirements. Therefore compareScreenShareMode is always true, even though we should create a new track.

The callback is then set to the wrong track, the old one: https://github.com/GetStream/stream-video-flutter/blob/main/packages/stream_video/lib/src/call/call.dart#L2428-L2430

Debugging showed that on the actual track the onEnded callback was null: https://github.com/flutter-webrtc/dart-webrtc/blob/main/lib/src/media_stream_track_impl.dart#L16

🧪 Testing

Test by running on web and start screen sharing only tabs and stop them using the browser tools.

☑️Contributor Checklist

General

• Assigned a person / code owner group (required)
• Thread with the PR link started in a respective Slack channel (#flutter-team) (required)
• PR is linked to the GitHub issue it resolves

☑️Reviewer Checklist

• Sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• All code we touched has new or updated Documentation