Port dereference functionality from 1.x to 2.x

[MikeEdgar]

Dereferencing functionality was previously in version 1.x [1 & 2], but not ported to 2.x. This issue is to track the porting of the feature to the 2.x series.

[1] https://github.com/Apicurio/apicurio-data-models/tree/1.1.27/src/main/java/io/apicurio/datamodels/openapi/visitors/dereference
[2] https://github.com/Apicurio/apicurio-data-models/blob/1.1.27/src/main/java/io/apicurio/datamodels/Library.java#L303-L343

[EricWittmann]

Started working on this a little bit, FYI.

[EricWittmann]

Early draft of this functionality for a-d-m version 2.x is here:

#669

@MikeEdgar @jsenko