[dart][dart-dio] Prevent name collisions for fields with leading _ (!14709) · Merge requests · OpenAPI Tools / openapi-generator

leading underscores _ mark private fields in Dart, so until now we just removed them
but just removing the fields can lead to name collision and missing fields
a prominent use-case are fields id and _id which previously would result in the _id field being lost on the Dart side
fixes #14482

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