src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts/NotebookEditorWidget/updateEditorFocus
class NotebookEditorWidget:	updateEditorFocus() {
		// Note - focus going to the webview will fire 'blur', but the webview element will be
		// a descendent of the notebook editor root.
		const focused = DOM.isAncestor(document.activeElement, this._overlayContainer);
		this._editorFocus.set(focused);
		this.viewModel?.setEditorFocus(focused);
	}