insertionOf function
gets the insertion point relative to globalOffset, necessary for rearranging order through drag and drop.
Implementation
InsertionPoint insertionOf(GlobalKey key, Offset globalOffset) {
return (key.currentContext!.findRenderObject() as InsertableWrapRender)
.insertionIndexAt((key.currentContext!.findRenderObject() as RenderBox)
.globalToLocal(globalOffset));
}