[BUG] Core java schema classes missing schema required property names + requiredVars values

[spacether]

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

Core classes that store schemas:

• CodegenModel
• CodegenProperty
• CodegenParameter
• CodegenResponse

are missing schema.required information which is a list of strings
At first glance it looks like requiredVars may contain this info but that's not true
That only stores properties whose names are in required.
So if a property is an additionalProperty (not defined in properties) then it does not make it into requiredVars
@wing328
@jimschubert
@cbornet
@ackintosh
@jmini
@etherealjoy
@sebastien-rosset

Feature: jsonschema.required

openapi-generator version

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Add requiredPropertyNames to:

• CodegenModel
• CodegenProperty
• CodegenParameter
• CodegenResponse

[spacether]

This PR: #8962
adds a hasRequired boolean and adds tests showing that this data is missing from many of our java schema classes.

[spacether]

This issue came up when working on #12619
The codegenModel for the component RequiredWithEscapedCharacters in the schema below:

openapi: 3.0.3
info:
  title: openapi 3.0.3 sample spec
  description: sample spec for testing openapi functionality, built from json schema
    tests for draft6
  version: 0.0.1
paths: {}
components:
  schemas:
    RequiredWithEscapedCharacters:
      required:
      - 'foo

        bar'
      - foo"bar
      - foo\bar
      - "foo\rbar"
      - "foo\tbar"
      - "foo\fbar"

Does not have any requiredVars generated for it.