[maps] fix open legend button icon is only partially visible (#233892)

Closes #233889

<img width="136" height="121" alt="Screenshot 2025-09-03 at 9 52 40 AM"
src="https://github.com/user-attachments/assets/3bf6db56-e07d-4483-9c4a-62bc0efb8ccd"
/>

Co-authored-by: Elastic Machine <[email protected]>

Author: nreese

x-pack/platform/plugins/shared/maps/public/connected_components/right_side_controls/layer_control/_layer_control.scss

@@ -20,6 +20,7 @@
 .mapLayerControl__addLayerButton,
 .mapLayerControl__openLayerTOCButton {
   pointer-events: all;
+  padding: 0 $euiSizeS;
 
   &:enabled,
   &:enabled:hover,