[BUG][GO] Imports for field types are not included when using inheritance/polymorphism

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
  In the generated model_foo.go, we have

    import (
    	"encoding/json"
    )
  

  But should have

  import (
  	"encoding/json"
  	"time"
  )
  

• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

I found a case where the generated Go code doesn't compile, it is missing an import of the time package. I think it's due to an incorrect implementation of polymorphism.

openapi-generator version

$ docker run --rm openapitools/openapi-generator-cli:latest version
7.10.0-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  version: '1.0.0'
  title: 'FooBar Service'
paths: {}
components:
  schemas:
    Foo:
      type: object
      anyOf: [] # doesn't need to contain anything, the object's properties are dropped due to the presence of anyOf
      properties:
        bar:
          format: date-time
          type: string

Generation Details

I'm using

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate \
        --input-spec /local/go-time-import.yaml \
        --generator-name go \
        --additional-properties "withGoMod=false" \
        --package-name gen \
        --output /local/gen

Steps to reproduce

If you run https://gist.github.com/perhallgren/d2af2441d7c265a06407313b064f68d6, you get:

[...]
gen/model_foo.go:22:7: undefined: time
gen/model_foo.go:43:24: undefined: time
gen/model_foo.go:45:11: undefined: time
gen/model_foo.go:53:28: undefined: time
gen/model_foo.go:70:24: undefined: time

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/issues/19958

Suggest a fix

I'm working on https://github.com/OpenAPITools/openapi-generator/pull/19958, with a fix that seems to solve the problem I am having.

Start with the OpenAPI declaration and generation command in the issue, then inspect the generated gen/model_foo.go output and compare the proposed fix in PR #19958. Done means the generated Go model includes the required time import and compiles without the reported undefined: time errors.