[ES|QL] fix editor menus on safari (#218167)

## Summary

Fix https://github.com/elastic/kibana/issues/215405

Tooltips still work:

<img width="524" alt="Screenshot 2025-04-14 at 1 03 17 PM"
src="https://github.com/user-attachments/assets/5a28d2e4-af75-455f-9df1-691493460cc7"
/>

---------

Co-authored-by: Stratoula Kalafateli <efstratia.kalafateli@elastic.co>

src/platform/packages/private/kbn-esql-editor/src/esql_editor.tsx

@@ -776,7 +776,15 @@ export const ESQLEditor = memo(function ESQLEditor({
           </EuiFlexItem>
         </EuiFlexGroup>
       )}
-      <EuiFlexGroup gutterSize="none" responsive={false} ref={containerRef}>
+      <EuiFlexGroup
+        gutterSize="none"
+        css={{
+          zIndex: theme.euiTheme.levels.flyout,
+          position: 'relative',
+        }}
+        responsive={false}
+        ref={containerRef}
+      >
         <EuiOutsideClickDetector
           onOutsideClick={() => {
             setIsCodeEditorExpandedFocused(false);