HarmonyOS swiper的controller不能changeIndex，只能前后切

Swiper组件的index属性支持状态绑定，从而实现跳转到指定index；

@State currentIndex: number = 0
Swiper(this.swiperController) {
}
.index(this.currentIndex)
.onChange((index: number) => {
  this.currentIndex = index
})
Button('to index 3')
  .onClick(() => {
    this.currentIndex = 3
  })