src/vs/workbench/contrib/notebook/browser/notebookEditor.ts/NotebookEditor/clearInput
class NotebookEditor:	override clearInput(): void {
		this._inputListener.clear();

		if (this._widget.value) {
			this._saveEditorViewState(this.input);
			this._widget.value.onWillHide();
		}
		super.clearInput();
	}