Transform JSON for dataType/paramType mixup.

Summary:
Now understanding the nature of the swagger-core bug around
dataType and paramType parsing, avoid forking the code and just
continue the practice of working around it by transforming the
JSON into the format swagger-core is expecting. Within a
parameter, rename the "paramType" field to "type" and the "type"
field to "dataType".

In the process, restructure the match ladder a bit so it's not
so unwieldy.

Test Plan:
Generated files look the same according to git diff, and they
still compile and work correctly.

Reviewers: j

Reviewed By: j

Subscribers: eng

Differential Revision: http://phabricator.scale-data.com/D962