Consider RangeReferenceFiles with transformations

Currently we have References used by HalfStoreReaders and HFileLinks.
For various use cases we have here we have need for a RangeReferences with simple transformation of the keys.
That would allow us to map HFiles between regions or even tables without copying any data.

We can probably combine HalfStores, HFileLinks, and RangeReferences into a single concept:

• RangeReference = arbitrary start and stop row, arbitrary key transformation
• HFileLink = start and stop keys set to the linked file's start/stop key, transformation = identity
• (HalfStore) References = start/stop key set according to top or bottom reference, transformation = identity

Note this is a brainstorming issue.
(Could start with just references with arbitrary start/stop keys, and do transformations later)