Handle persistence flags for extended attributes

[RhetTbull]

I don't believe persistence flags are properly handled (need to see how xattr deals with these):

https://eclecticlight.co/2020/11/02/controlling-metadata-tricks-with-persistence/

[RhetTbull]

At least on Catalina, attributes with these flags are not properly handled by Finder so they don't show up in Smart Folders, etc. So implementing these may not be worthwhile. From above linked article (and confirmed in my own testing):

The snag is that few Apple engineers seem aware of this valuable feature, so these flags usually aren’t handled correctly. Just as with the Finder now, com.apple.metadata:kMDItemComment#N should be treated as a xattr of type com.apple.metadata:kMDItemComment with the flag N. Instead, it’s treated as a xattr with a different name. Presumably this is because Apple never got round to properly documenting this unique system for managing the persistence of metadata, and it has simply been forgotten. By Apple’s own engineers.