Investigate the possibility of add-ons enhancing find references

There are certain situations where references to declarations may exist in a DSL form. For example, in Rails, if you were to rename/find references for a model, then associations made to that model should be included as well.

class Post
end

class User
  has_many :posts # <<< this should be counted as a reference to the `Post` class, despite being a symbol
end

We will need to study what use cases exist and how to allow for this. Maybe this should be a concern of indexing enhancements and we should expedite the work to merge the reference finder with the declaration listener.

Start by cataloguing the DSL reference use cases described in the issue, including Rails associations such as has_many :posts. Then investigate the indexing enhancements and the proposed merge of the reference finder with the declaration listener; done means an agreed design and implementation path for recognizing these references.