SimpleMVCCIterator.RangeKeys() currently returns []MVCCRangeKeyValue. However, this stack has a few special properties: it is ordered by timestamp (descending), and all range keys have the same bounds. We have a fair but of code which assumes []MVCCRangeKeyValue has these properties, so that it can e.g. do binary searches.

We should consider using a distinct type for these, e.g. MVCCRangeKeyStack, which is guaranteed to have these properties. Then e.g. FirstRangeKeyAbove() and HasRangeKeyBetween() would be methods of this type, and we could possibly omit the key bound duplication for each element.

Jira issue: CRDB-17344

Epic CRDB-2624