src/vs/workbench/api/common/extHostNotebookDocument.ts/ExtHostNotebookDocument/_changeCellLanguage
class ExtHostNotebookDocument:	private _changeCellLanguage(index: number, newModeId: string): void {
		const cell = this._cells[index];
		if (cell.apiCell.document.languageId !== newModeId) {
			this._textDocuments.$acceptModelModeChanged(cell.uri, newModeId);
		}
	}