LevelMeshEditor.cs

private GUIContent[] toolsButton;
private List<LevelMeshTool> tools;
private LevelMeshTool activeTool;
int m_selectedTool;
int selectedTool
{
    get => m_selectedTool;
    set
    {
        m_selectedTool = value;
        activeTool = tools[m_selectedTool];
    }
}

private void OnEnable()
{
  tools = LevelMeshToolProvider.tools;
  toolsButton = tools.Select(t => t.Content).ToArray();
}