src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts/BackLayerWebView/findHighlight
class BackLayerWebView:	async findHighlight(index: number): Promise<number> {
		const p = new Promise<number>(resolve => {
			const sub = this.webview?.onMessage(e => {
				if (e.message.type === 'didFindHighlight') {
					resolve(e.message.offset);
					sub?.dispose();
				}
			});
		});

		this._sendMessageToWebview({
			type: 'findHighlight',
			index
		});

		const ret = await p;
		return ret;
	}