[go-experimental] Fix oneOf generation of primitive types

Created by: zippolyte

Given the following spec

components:
  schemas:
    Something:
      type: object
      oneOf:
        - $ref: '#/components/schemas/One'
        - $ref: '#/components/schemas/Two'
        - $ref: '#/components/schemas/Three'
    One:
      type: string
    Two:
      type: integer
    Three:
      type: object
      properties:
        foo:
          type: integer

The go-experimental generator would generate the following struct

type Something struct {
        string *string
        int32  *int32
        Three  *Three
}

This fails because the field names int32 and string are reserved keywords.

I fixed it by Capitalizing the field name, but let me know if you think there is a better way to do this.

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