src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeView/handleDrag
class ExtHostTreeView:	async handleDrag(sourceTreeItemHandles: TreeItemHandle[], treeDataTransfer: IDataTransfer, token: CancellationToken): Promise<vscode.DataTransfer | undefined> {
		const extensionTreeItems: T[] = [];
		for (const sourceHandle of sourceTreeItemHandles) {
			const extensionItem = this.getExtensionElement(sourceHandle);
			if (extensionItem) {
				extensionTreeItems.push(extensionItem);
			}
		}

		if (!this.dndController?.handleDrag || (extensionTreeItems.length === 0)) {
			return;
		}
		await this.dndController.handleDrag(extensionTreeItems, treeDataTransfer, token);
		return treeDataTransfer;
	}