This is meant to address #863 which asks for x-go-type to work with $ref. It also fixes my use case which is for x-oapi-codegen-extra-tags like:

obj:
  type: object
  properties:
    start_port:
      $ref: '#/components/schemas/Port'
      x-oapi-codegen-extra-tags:
        bson: start_port
    end_port:
      $ref: '#/components/schemas/Port'
      x-oapi-codegen-extra-tags:
        bson: end_port

I have added tests in the internal/tests/extensions directory to cover a few of the extensions, I can add a complete list if desired.

We already treat x-order in this way (use the value next to the ref if provided) as of #1700 and this pr makes the functionality complete and consistent for all supported extensions.