chore: calculateDimensionsIndexRange should calculate on begining

[ryuever]

  calculateDimensionsIndexRange() {
    let startIndex = 0;
    const rangeMap: {
      [key: string]: number;
    } = {};
    this._dimensionsIndexRange = this.indexKeys.reduce((acc, key) => {
      const dimensions = this.getDimension(key);
      const recyclerType = dimensions.recyclerType;
      if (rangeMap[recyclerType] === undefined) rangeMap[recyclerType] = 0;

      const endIndex = startIndex + dimensions.length;
      const startIndexInRecycler = rangeMap[recyclerType];
      rangeMap[recyclerType] = startIndexInRecycler + dimensions.length;
      acc.push({
        startIndex,
        endIndex,
        dimensions,
        startIndexInRecycler,
        enIndexInRecycler: rangeMap[recyclerType],
      });
      startIndex = endIndex;
      return acc;
    }, []);
  }

  onItemsCountChanged(useCache = false) {
    this.reflowFlattenData();
    this.calculateDimensionsIndexRange();
    this.calculateReflowItemsLength();
    this.updateChildDimensionsOffsetInContainer();
    this.updateScrollMetrics(this._scrollMetrics, { useCache });
  }

Basically, calculateDimensionsIndexRange is triggered onItemsCountChanged, It will be about 50ms delay comparing with registerList / registerItem.

Now this issue will cause itemMeta.getIndexInfo() return with null