[ts][pixi-v8] Add removeSlotObjects function

[Zyie]

It would be great if there was a removeSlotObjects which removed all slot objects easily.
This would be consistent with pixi and its addChild, removeChild, removeChildren API

The implementation could be something like this:

public removeSpineObjects() {
  this.removeChildren();
  this._slotObjects = {}
}

I'm happy to do the PR if this is something you would like adding

[davidetan]

Hello!

I don't really know how much the slot objects feature is used, but it seems that Pixi users love it :D

I guess it might be handy to add removeSlotObjects.
You can definitely go on with the PR.
Maybe have a look at the pixi masks that are created when there are slot objects and a clipping attachment is active. Even though they should clean themselves automatically.