Revert rc-slider dependency update, add z-index to tooltip (#23873)

packages/grafana-ui/package.json

@@ -50,7 +50,7 @@
     "papaparse": "4.6.3",
     "rc-cascader": "1.0.1",
     "rc-drawer": "3.1.3",
-    "rc-slider": "9.2.3",
+    "rc-slider": "8.7.1",
     "rc-time-picker": "^3.7.3",
     "react": "16.12.0",
     "react-beautiful-dnd": "13.0.0",

packages/grafana-ui/src/components/Slider/Slider.tsx

@@ -75,6 +75,7 @@ const getStyles = stylesFactory((theme: GrafanaTheme, isHorizontal: boolean) =>
       .rc-slider-tooltip {
         cursor: grab;
         user-select: none;
+        z-index: ${theme.zIndex.tooltip};
       }
 
       .rc-slider-tooltip-inner {