TODO: implement the customized scrollTo method for x-swiper

in the file packages/web-platform/web-elements/src/XSwiper/XSwiper.ts

• remove scrollToNext
• remove scrollToPrevious
• add a new method scrollTo, overrides the default one

The new scrollTo method should compatiable with the HTML's usage and the new usage.

The new usage with one parameter:

{
     index: number, // target index
     smooth: boolean = true, // Whether there is switching animation
   }