[Avro] Rename VisitorFormatWrapperImpl to AvroFormatVisitorWrapper in 2.14 or 3.0

[MichalFoksa]

VisitorFormatWrapperImpl class name is unfortunate. It makes sense to rename it into something more descriptive, for example AvroFormatVisitorWrapper.

Implementation in 2.13:

public class VisitorFormatWrapperImpl
    implements JsonFormatVisitorWrapper

Citation from #292 comment:

Maybe it would make sense to also file a follow-up issue about actual renaming (of VisitorFormatWrapperImpl ) like you suggested first (to AvroFormatVisitorWrapper).
I'd have to think if it actually could go in 2.14, after all, or at least in 3.0.

Question is, in which release?