[BUG] [dart-dio] _id is generated as id

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

When generating a model a property _id is transformed and becomes id in the resulting dart class. In the provided example this breaks the class as it already has another id property.

I tested this on latest master with this command (hosting the yml on a public gist):

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate \
        -i https://gist.githubusercontent.com/flodaniel/65ffdf1e803773606dc42dccd58ba021/raw/7ce9e4e7721e1df9bb28c7d2de94581351f387ad/gistfile1.txt -g dart-dio -o /local/out/bad_id_generation

openapi-generator version

openapi-generator-cli 6.2.1
commit : b0ce532
built : 2022-11-01T09:40:00Z
source : https://github.com/openapitools/openapi-generator
docs : https://openapi-generator.tech/

OpenAPI declaration file content or url

https://gist.github.com/flodaniel/65ffdf1e803773606dc42dccd58ba021

openapi: 3.0.0
info:
  title: Bad _id generation
  version: 0.0.1
paths: {}
tags: []
servers: []
components: 
  schemas:
    ConflictingIdProperty:
      type: object
      properties:
        id:
          type: string
        _id:
          type: string

Generation Details

openapi-generator generate -i ./bad_id_generation.yml -g dart-dio -o ./bad_id_generation

Steps to reproduce

1. Run the generation
2. review the resulting conflicting_id_property.dart file with the conflicting id properties.

Related issues/PRs

Suggest a fix

The issue is probably within class.mustache (https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache). baseName is correct but name is missing the _.

Start with modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache, then reproduce the issue using the provided OpenAPI gist and dart-dio generation command. Review the generated conflicting_id_property.dart file; done means the _id and id properties remain distinct in the generated Dart class.