[BUG] The runtime-type specified in instantiation-types option is not respected

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?

Description

The OpenAPI Generator does not generate the runtime-type specified in the --instantiation-types mapping option. The generated code defaults to the default runtime-time ArrayList for array and HashMap for map.

openapi-generator version

3.3.4, 4.0.0-beta3

OpenAPI declaration file content or url

Pet:
  type: object
  properties:
    owners:
      type: array
      items:
        $ref: "#/components/schemas/Owner"
Owner:
  type: object
  properties:
     name:
        type: string
  ....
  ....

Command line used for generation

openapi-generator generate -i petstore.yaml -g java --instantiation-types=array=HashSet --type-mappings=array=Set --import-mappings=HashSet=java.util.HashSet

Steps to reproduce

Generate code with the above-specified command

Generated code in Pet.java

public Pet addOwnersItem(Owner ownersItem) {
  if (this.owners == null) {
    this.owners = new ArrayList<Owner>();
  }
  this.owners.add(ownersItem);
  return this;
}

Expected code

public Pet addOwnersItem(Owner ownersItem) {
  if (this.owners == null) {
    this.owners = new HashSet<Owner>();
  }
  this.owners.add(ownersItem);
  return this;
}

Related issues/PRs

None

Suggest a fix

Suggest fix would be to correctly interpret instantiation-types and import-mappings options and adjust code-gen logic to generate appropriate runtime type.

Reproduce the issue with the openapi-generator generate command and the supplied OpenAPI declaration, then inspect how the Java generator handles --instantiation-types, --type-mappings, and --import-mappings. Compare the generated Pet.java initializer with the expected HashSet<Owner> form; done means the configured runtime type is emitted instead of ArrayList.