[v9.4.x] BarChart: Only apply radius to topmost bar segment when stacking (#63986)

BarChart: Only apply radius to topmost bar segment when stacking (#63906)

(cherry picked from commit 9314fe1056)

Co-authored-by: Leon Sorokin <leeoniya@gmail.com>

public/app/plugins/panel/barchart/bars.ts

@@ -286,7 +286,14 @@ export function getConfig(opts: BarsOptions, theme: GrafanaTheme2) {
     : {};
 
   let barsBuilder = uPlot.paths.bars!({
-    radius: barRadius,
+    radius: pctStacked
+      ? 0
+      : !isStacked
+      ? barRadius
+      : (u: uPlot, seriesIdx: number) => {
+          let isTopmostSeries = seriesIdx === u.data.length - 1;
+          return isTopmostSeries ? [barRadius, 0] : [0, 0];
+        },
     disp: {
       x0: {
         unit: 2,