Extract expandChild a to VivideObject

[onsetsu]

expandChild asynchronously fetches the child layer of a VivideObject.

Having a VivideView dynamically setting the expandChild method onto a widget, seems counterintuitive.

Instead, this method should be exposed by the VivideObject itself:

childLayer = await vivideObject.getChildren();

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Also, a widget should not be in charge of setting the childLayer of a VivideObject:

object.childLayer = await this.expandChild(childData, childLayer.script);