[typescript] allOf with multiple values is not handled properly

Created by: Fredx87

Description

If a schema is defined with the allOf operator with multiple values, the generated model is an interface that extends only the first value.

openapi-generator version

3.2.2

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: TestApi
  version: 1.0.0
paths:
  /test:
    get:
      summary: Test
      operationId: testApi
      responses:
        "200":
          description: Ok
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ModelC"
components:
  schemas:
    ModelA:
      properties:
        foo:
          type: string
    ModelB:
      properties:
        bar:
          type: string
    ModelC:
      allOf:
        - $ref: "#/components/schemas/ModelA"
        - $ref: "#/components/schemas/ModelB"
        - type: object
          properties:
            baz:
              type: string

Command line used for generation

docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli:v3.2.2 generate -i /local/swagger.yaml -g typescript-angular -o /local/ts-angular -DngVersion=6.0 docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli:v3.2.2 generate -i /local/swagger.yaml -g typescript-fetch -o /local/ts-fetch

Suggest a fix/enhancement

The model generated for ModelC is the following interface:

export interface ModelC extends ModelA { 
    baz?: string;
}

When it should be:

export interface ModelC extends ModelA, ModelB { 
    baz?: string;
}