src/vs/workbench/common/editor.ts/findViewStateForEditor
export function findViewStateForEditor(input: EditorInput, group: GroupIdentifier, editorService: IEditorService): object | undefined {
	for (const editorPane of editorService.visibleEditorPanes) {
		if (editorPane.group.id === group && input.matches(editorPane.input)) {
			return editorPane.getViewState();
		}
	}

	return undefined;
}