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Continue Tuple API refactoring

- Renamed methods on staticclass FdbTuple to be in synch with the new naming conventions
- FdbTuple.EncodeKey() *could* be used to encoded values, but the name suggest that it tries to keep ordering properties that may be overkill for values
- Simplified names with replacing "Range" by either the plural (EncodeKeys) or nothing if there are no overload resolution ambiguity possible