refactor: propose G6 layout standard and adapt antv/layout

[Aarebecca]

• 定义 G6 的布局标准接口，如下 / Define the layout standard interfaces for G6 as follows

interface BaseLayout {
  execute(model: GraphData, options?: STDLayoutOptions): Promise<GraphData>;

  // suitable for iterative layouts
  stop?: () => void;
  tick?: (data: GraphData) => void;
}

• 适配 @antv/layout 为 G6 布局 / Adapt @antv/layout to G6 layout
• 流水线布局属性 nodesFilter 变更为 nodeFilter / The property of pipeline layout nodesFilter is renamed to nodeFilter
• 添加了自定义布局示例 / Add demo that custom layout