feat: Adds a separator to Select All option (#22776)

superset-frontend/.storybook/preview.jsx

@@ -87,5 +87,5 @@ addParameters({
       ],
     },
   },
-  controls: { expanded: true },
+  controls: { expanded: true, sort: 'alpha' },
 });

superset-frontend/src/components/Select/Select.tsx

@@ -467,6 +467,7 @@ const Select = forwardRef(
           {selectAllEnabled && (
             <Option
               id="select-all"
+              className="select-all"
               key={SELECT_ALL_VALUE}
               value={SELECT_ALL_VALUE}
             >

superset-frontend/src/components/Select/styles.tsx

@@ -52,7 +52,9 @@ export const StyledSelect = styled(AntdSelect, {
     .ant-select-arrow .anticon:not(.ant-select-suffix) {
       pointer-events: none;
     }
-
+    .select-all {
+      border-bottom: 1px solid ${theme.colors.grayscale.light3};
+    }
     ${
       oneLine &&
       `