feat: support nullable field of combine schemas

[keita1714]

Summary

This PR solves the problem that nullable field for combine schemas(oneOf, anyOf, allOf) is not enabled.

Test Plan

The following yaml is processed correctly.

openapi: 3.0.0
info:
  version: 1.0.0
paths:
  /test:
    post:
      operationId: Test
      requestBody:
        content:
          application/json:
            schema:
              allOf:
                - $ref: '#/components/schemas/SchemaA'
                - $ref: '#/components/schemas/SchemaB'
              nullable: true
      responses:
        '200':
          content:
            application/json:
              schema:
                type: string
components:
  schemas:
    SchemaA:
      type: object
      required:
        - a
      properties:
        a:
          type: integer
          format: int32
    SchemaB:
      type: object
      required:
        - b
      properties:
        b:
          type: string

[Himenon]

Thank you very much.

[Himenon]

Already Published !

• https://github.com/Himenon/openapi-typescript-code-generator/releases/tag/%40himenon%2Fopenapi-typescript-code-generator%400.10.1