Support models with multi-level hierarchy (via roxspring) (#4503)

* Example of broken multi-level hierarchy

* Support for multiple levels of hierarchy in model objects

* Support for multiple levels of hierarchy in generators

* Regenerated samples

* Temporarily skip scalaz sample verification, which is having issue with Java version in CI container

* Re-enable scalaz in verify samples

Co-authored-by: Rob Oxspring <roxspring@imapmail.org>

samples/server/petstore/php-slim/lib/Model/BigCat.php

@@ -0,0 +1,39 @@
+<?php
+/**
+ * BigCat
+ *
+ * PHP version 7
+ *
+ * @package OpenAPIServer\Model
+ * @author  OpenAPI Generator team
+ * @link    https://github.com/openapitools/openapi-generator
+ */
+
+/**
+ * NOTE: This class is auto generated by the openapi generator program.
+ * https://github.com/openapitools/openapi-generator
+ */
+namespace OpenAPIServer\Model;
+
+/**
+ * BigCat
+ *
+ * @package OpenAPIServer\Model
+ * @author  OpenAPI Generator team
+ * @link    https://github.com/openapitools/openapi-generator
+ */
+class BigCat
+{
+    
+    /** @var string $className */
+    private $className;
+    
+    /** @var string $color */
+    private $color;
+    
+    /** @var bool $declawed */
+    private $declawed;
+    
+    /** @var string $kind */
+    private $kind;
+}

samples/server/petstore/php-slim/lib/Model/BigCatAllOf.php

@@ -0,0 +1,30 @@
+<?php
+/**
+ * BigCatAllOf
+ *
+ * PHP version 7
+ *
+ * @package OpenAPIServer\Model
+ * @author  OpenAPI Generator team
+ * @link    https://github.com/openapitools/openapi-generator
+ */
+
+/**
+ * NOTE: This class is auto generated by the openapi generator program.
+ * https://github.com/openapitools/openapi-generator
+ */
+namespace OpenAPIServer\Model;
+
+/**
+ * BigCatAllOf
+ *
+ * @package OpenAPIServer\Model
+ * @author  OpenAPI Generator team
+ * @link    https://github.com/openapitools/openapi-generator
+ */
+class BigCatAllOf
+{
+    
+    /** @var string $kind */
+    private $kind;
+}