Add support for Unity UI Toolkit in Unity 6

[tomashined]

Hello. I need to add a simpler connection with the UI Toolkit. That is, either you should create your own Custom Controls to display video, or simplify the way I'm doing it now... I'm currently doing it like this: after getting the first frame from the camera, I pass "VideoKitCameraManager.texture as Texture2D" to the VisualElement through the standard assignment "style.backgroundImage = new StyleBackground(texture)".