fix(sidebar): scroll animation not working with sidebarDuration prop (#3169)

Author: Miles-hxy

src/packages/sidebar/sidebar.taro.tsx

@@ -111,14 +111,26 @@ export const SideBar: FC<Partial<TaroSideBarProps>> & {
   const titleRectRef = useRef<RectItem[]>([])
   const [scrollTop, setScrollTop] = useState(0)
   const scrollDirection = (to: number) => {
+    if (sidebarDuration === 0) {
+      setScrollTop(to)
+      return
+    }
+
+    const from = scrollTop
+    const frames = Math.round(sidebarDuration / 16)
     let count = 0
-    const frames = sidebarDuration === 0 ? 1 : Math.round(sidebarDuration / 16)
+
     function animate() {
-      setScrollTop(to)
-      if (++count < frames) {
+      const progress = count / frames
+      const current = from + (to - from) * progress
+      setScrollTop(current)
+
+      if (count < frames) {
+        count++
         raf(animate)
       }
     }
+
     animate()
   }
   const scrollIntoView = (index: number) => {