Test DataContractSerializer with flags enum. Covers #21072.
When serializing an enum value, matching flags should not be consider when there is a flag that matches exactly.
Fixed how EnumMap serializes flag values. Fixes #21072.
While serializing an enum value, EnumMap no longer considers partial matching flags when there is a flag that matches exactly.
Merge pull request #1431 from esdrubal/enummap

Fixed how EnumMap serializes flag values.