Add a rule to check that the schemas for all 2XX responses are the same

[mikekistler]

For client generation, we want to have only one type of object returned from an operation. In terms of the REST API, that means that all the success response codes (2XX) should have the same schema.

Comparing schemas for equality might be a little tricky, so we could simplify the logic somewhat:

• An operation cannot return 200/201 and 204
• We don't need to check 202 since az-lro-reponses-codes flags any 2XX for an operation that returns 202

Maybe we'll start with that.