Make AkCollator.getString() use collator's decode if it finds a byte array

This makes case-insensitive BloomFilter cases that worked when CStringKeyCoder was used work when it is not.
It does not fix the cases that did not work, which now consistently (and wrongly) use the hex result of decodeSortKeyBytes(), either from CStringKeyCoder.decodeKeySegment() or from AkCollator.getString().

I think the correct fix for those requires distinguishing at the type level (perhaps via an instance attribute) that the values in an index row are byte arrays (or CStrings, which amounts to the same thing) representing a collator-encoded comparable value.