Add scene focus script

[zuedev]

Draft:

#if UNITY_EDITOR
using UnityEditor;

[InitializeOnLoad]
public static class KeepSceneFocusedOnPlay
{
    static KeepSceneFocusedOnPlay()
    {
        EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
    }

    private static void OnPlayModeStateChanged(PlayModeStateChange state)
    {
        if (state == PlayModeStateChange.EnteredPlayMode)
        {
            SceneView.FocusWindowIfItsOpen(typeof(SceneView));
        }
    }
}
#endif