Prometheus: fix popup positioning in monaco-based query-field (#38964)

* prometheus: monaco: fix popup positioning

* added explanation comment

public/app/plugins/datasource/prometheus/components/monaco-query-field/MonacoQueryField.tsx

@@ -16,6 +16,9 @@ const options: CodeEditorMonacoOptions = {
   scrollBeyondLastLine: false,
   renderLineHighlight: 'none',
   fontSize: 14,
+  // we need `fixedOverflowWidgets` because otherwise in grafana-dashboards
+  // the popup is clipped by the panel-visualizations.
+  fixedOverflowWidgets: true,
 };
 
 const MonacoQueryField = (props: Props) => {