UnsafeKVExternalSorter

Used by TungstenAggregationIterator, and WriteOutput, etc.,can be created by UnsafeFixedWidthAggregationMap.destructAndCreateExternalSorter

Internally use UnsafeExternalSorter for implementation. It allows optionally passing in a BytesToBytesMap directly in order to perform in-place sorting of records in the map.