[BUG][Java] useAbstractionForFiles does not work properly on docs .md

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

Description

useAbstractionForFiles changes File by org.springframework.core.io.Resource as the return type in the api classes.
This was done in the following MR: https://github.com/OpenAPITools/openapi-generator/pull/13168/files

However in the documentation files generated in markdown, the return type it's still File, and the example code doesn't use a org.springframework.core.io.Resource

openapi-generator version

7.8.0

Steps to reproduce

Use property useAbstractionForFiles = true

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/10665

Suggest a fix

I think the documentation files should use org.springframework.core.io.Resource if useAbstractionForFiles=true
And the example code snippet should be modified accordingly

Start by reproducing the Java generation with useAbstractionForFiles=true and inspect the generated Markdown documentation and example code. Compare their File types with the API classes changed by pull request 13168; done means the Markdown return type and example use org.springframework.core.io.Resource consistently.