Method setSelection

src/core/nodeviews/code-block.ts:1822–1827

* 设置选区

(anchor: number, head: number)

   * 设置选区
   */
  setSelection(anchor: number, head: number): void {
    this.cm.focus();
    this.cm.dispatch({
      selection: { anchor, head },
    });
  }

  /**
   * 选区是否在此节点内