fix (DefaultGenerator): Handle "$ref" parameter reference to identify parameter ID (#20239)

[JPPortier]

Fix proposal for #20239

Use ref field when filled in place of missing name:in to avoid collision onto generated id (when $ref is present, it generate systemically null:null ID)

So, with fix, in place of generating a missing parameter onto function prototype:

  public void get(Integer queryParameter) throws ApiException {

It now generated the correct list:

  public void get(String pathParameter, Integer queryParameter) throws ApiException {

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[wing328]

thanks for the PR

cc @OpenAPITools/generator-core-team

[wing328]

tested locally to confirm the fix.

let's give it a try

i'll try to add a test later

[wing328]

update: merged #20256 to add a test covering the issue moving forward