Tech debt: ModelElement.features may be confused with FeatureSet

[srawlins]

FeatureSet is the new analyzer (or Dart language) concept for enabled language features. As such, it may be a good idea to rename the features field (and related fields) on ModelElement.

This isn't a huge issue alone (there are plenty of other naming collisions about), but I was thinking of introducing a new class for ModelElement "features" which would encapsulate Strings (typically from keywords, like final, covariant, or from other situations, like inherited, read-only, etc.) and annotations (@protected, etc.). Going down the path of creating a class, like Feature or ElementFeature, etc, is now increasing the collision with FeatureSet.

So, what might be a new name? "Property" is already used for fields, so maybe "Attribute"? I don't think that is used elsewhere. So I might add new classes, "ElementProperty," "StringElementProperty", "AnnotationElementProperty."

[parlough]

I originally would say Modifier as I think of final and covariant as modifiers, but the fact we use it for labels such as inherited as well makes me think Attribute would be better.

[jcollins-g]

We could consider eliminating the Property/Field naming inconsistency within dartdoc and fully aligning with analyzer, calling them "Fields". That would free up "property" to be used here.

If that's going to still be too confusing, however, Attribute is a reasonable choice.