ResolveFully does not resolve MapSchema

[douglasbgray]

When using ParserOption.resilveFully(true) and the response schema is a map (or uses a schema that contains a map), the references are not fully resolved and left as $ref

Example:

openapi: 3.0.0
servers:
  - url: 'http://localhost:8080/sample'
info:
  description: A simple API to learn how to write OpenAPI Specification
  version: 1.0.1
  title: Simple API
paths:
  /sample:
    get:
      tags:
        - Sample
      operationId: getSample
      responses:
        '200':
          description: Sample
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/MyModelMap'
components:
  schemas:
    MyModel:
      type: object
      properties:
        name:
          type: string
    MyModelMap:
      type: object
      additionalProperties:
        $ref: "#/components/schemas/MyModel"

When this code is run against this schema:

ParseOptions options = new ParseOptions();
options.setResolveFully(true);
OpenAPI openAPI = new OpenAPIV3Parser().readLocation("openapi.yaml", null, options).getOpenAPI();
String yaml = Yaml.pretty(openAPI);

Results in this output:

openapi: 3.0.0
info:
  title: Simple API
  description: A simple API to learn how to write OpenAPI Specification
  version: 1.0.1
servers:
- url: http://localhost:8080/sample
paths:
  /sample:
    get:
      tags:
      - Sample
      operationId: getSample
      responses:
        200:
          description: Sample
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                  $ref: '#/components/schemas/MyModel'
components:
  schemas:
    MyModel:
      type: object
      properties:
        name:
          type: string
    MyModelMap:
      type: object
      additionalProperties:
        $ref: '#/components/schemas/MyModel'

I have created this PR with the fix and corresponding test:

#1124

[gracekarina]

thanks for this fix. Closing the issue with the merge of #1124