#24723 [core] Remove backslash from path

fyi @OpenAPITools/generator-core-team

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Summary by cubic

Normalizes generated operation paths by stripping backslashes in DefaultCodegen. Previously paths kept backslashes (e.g., /fake/path/backslash/GetPetById()); now they are removed (e.g., /fake/path/backslash/GetPetById()), preventing escaped characters from leaking into generated clients and docs.

• Review notes

  • Implemented in fromOperation by setting op.path = op.path.replace("\\", "").
  • Added an OAS 3.1 petstore path with backslashes and updated Java okhttp-gson-3.1 samples (README.md, docs/FakeApi.md, api/openapi.yaml, FakeApi.java) to show the normalized path.

• Migration

  • If your API requires literal backslashes in paths, they will now be removed. Avoid backslashes in OpenAPI paths or customize the generator to preserve them.