add a feature support for GridView when it jump to specified index, now we can set isFixedHeight with true.
for GridView items of fixed height, there's no longer need to calculate with sliding, but calculates height and spacing, directly jumping to the specified position
add a feature support for GridView when it jump to specified index, now we can set isFixedHeight with true.
for GridView items of fixed height, there's no longer need to calculate with sliding, but calculates height and spacing, directly jumping to the specified position