src/vs/workbench/api/browser/mainThreadTreeViews.ts/TreeViewDragAndDropController/onDrop
class TreeViewDragAndDropController:	onDrop(treeItem: ITreeItem[], targetTreeItem: ITreeItem): Promise<void> {
		return this._proxy.$onDrop(this.treeViewId, treeItem.map(item => item.handle), targetTreeItem.handle);
	}