message: feature: add `group.replaceAt()`
diff: @@ -108,6 +108,25 @@ class Group extends Element<GroupProps> {
  return this;
  }
  + replaceAt(child: Element, index: number) {
  + const children = this._children;
  + const old = children[index];
  +
  + if (child && child !== this && child.parent !== this && child !== old) {
  + children[index] = child;
  +
  + old.parent = null;
  + const zr = this.__zr;
  + if (zr) {
  + old.removeSelfFromZr(zr);
  + }
  +
  + this._doAdd(child);
  + }
  +
  + return this;
  + }
  +
  _doAdd(child: Element) {
  if (child.parent) {
  // Parent must be a group
  