Make Generated Builders Vec-Aware (#267)

* Make Generated Builders Vec-Aware

This updates the generated builders & fluent client to be vec-aware. The builder method with the same name as the field will append the field to the list, creating it if it doesn't exist. A `set_xyz` method is added which retains the original behavior.

* Fix test usages of builders

* Add Map builder

* Fix unit tests

* Add impl Into clause for builder helpers

* Update another test

* One more spot that needed to be updated

* Delete dead code