Referencing self:: constants in annotations

At the moment constant parsing doesn't read `self::` constants and I have a use case where that would be the most practical solution:
I would like to pass serialization groups for a property that's defined in a trait. Since not all entities will have the same serialization groups for the properties in the traits, the only currently available options that I see is to either repeat the property definition in each entity or repeat the groups serialization definition for each property and each entity in yaml/xml.

I would have created a PR instead of an issue for this, but from what I see in the DocParser class, the only way to get the original class name would be to parse the context string, which seems like a bad idea. I'm hoping that someone more familiar with the codebase could do it in a cleaner way. If there isn't a better way, please let me know and I'll make a PR.