addChild method
Add a child at a given position with a widget. Returns the child ID. You need the child size for optimising the focus on child
Implementation
CanvasChildId addChild(Offset position, Widget widget, {Size? childSize, CanvasChildId? id}) {
final childId = _addChildInternal(position, widget, childSize: childSize, id: id);
markDirty();
return childId;
}