Describes how much content the sliver should provide starting from the cacheOrigin.
Not all content in the remainingCacheExtent will be visible as some of it might fall into the cache area of the viewport.
The remainingCacheExtent is always larger or equal to the remainingPaintExtent. Content, that falls in the remainingCacheExtent, but is outside of the remainingPaintExtent is currently not visible in the viewport.
- RenderViewport.cacheExtent for a description of a viewport's cache area.
final double remainingCacheExtent