[BUG][aspnetcore] language specific primitive model is created in v5.4.0

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?
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Description

We have the language-specific-primitive NodaTime.LocalDate. Since the upgrade to v5.4.0 a model NodaTime.LocalDate is created which is not the expected output. The expected output is that no LocalDate model is created because we use the .NET library. In v5.3.0 everything works

openapi-generator version

5.4.0

OpenAPI declaration file content or URL

config:

aspnetCoreVersion: 5.0
isLibrary: true
newtonsoftVersion: 5.0.6
operationIsAsync: false
packageName: Brokkoli.Api
sourceFolder: ""
useDateTimeOffset: false
useDefaultRouting: false
useSwashbuckle: false
operationResultTask: true
operationModifier: abstract
classModifier: abstract
nullableReferenceTypes: true
importMappings:
  LocalDate: NodaTime.LocalDate
typeMappings:
  LocalDate: NodaTime.LocalDate

excerpt from specification:

...
        shippingDate:
          $ref: "#/components/schemas/LocalDate"
...
    LocalDate:
      x-csharp-value-type: true
      type: object
...

Generation Details

openapi-generator generate -i api.yml -t aspnetcore-generator-template -g aspnetcore -c openapi-server-generator.yml --model-name-suffix Dto --language-specific-primitives=NodaTime.LocalDate

Start by reproducing the issue with the shown openapi-generator generate command, configuration, and LocalDate schema, comparing generation in v5.3.0 and v5.4.0. Trace handling of language-specific-primitives, importMappings, and typeMappings for the aspnetcore generator. Done means the NodaTime.LocalDate mapping no longer creates a LocalDate model.