[Go] Prevent naming collisions between model properties and generated getter/setter methods

Created by: DouglasDwyer

This PR adds a small fix for naming collisions in Go between generated struct fields and getter/setter method names. When using the Go generator, specifications that include model properties like Area and HasArea will cause code to be generated with compilation errors. This occurs because the HasArea field on the generated model has the same name as the HasArea() function for checking whether the model contains an Area property. This change adds a conflict resolution method which automatically renames model fields by appending underscore characters (_) to them until no more naming conflicts occur (without changing the underlying JSON names).

Here is a simple example of a specification which causes issues:

openapi: 3.0.1
info:
  title: Test REST API
  description: ''
  termsOfService: ''
  version: 0.0.0
paths: {}
components:
  schemas:
    Broken:
      type: object
      properties:
        hasMass:
          type: boolean
        mass:
          type: array
          items:
            type: number
            format: double

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