[New feature] Allowing the `ListView` slivers to have different extents while still having scrolling performance (#131393)

Fixes https://github.com/flutter/flutter/issues/113431

Currently we only support specifying all slivers to have the same extent.
This patch introduces an `itemExtentBuilder` property for `ListView`, allowing the slivers to have different extents while still having scrolling performance, especially when the scroll position changes drastically(such as scrolling by the scrollbar or controller.jumpTo()).

@Piinks Hi, Any thoughts about this?  :)