src/vs/workbench/contrib/notebook/browser/viewModel/notebookViewModel.ts/NotebookViewModel/selectionHandles
class NotebookViewModel:	private get selectionHandles() {
		const handlesSet = new Set<number>();
		const handles: number[] = [];
		cellRangesToIndexes(this._selectionCollection.selections).map(index => this.cellAt(index)).forEach(cell => {
			if (cell && !handlesSet.has(cell.handle)) {
				handles.push(cell.handle);
			}
		});

		return handles;
	}