Openapi big model hierarchy defect

[mhodovaniuk]

This PR aim to fix #3361 by making sure that Schema.Transform are not ignored.

This also fixes an issue where a reference was used instead of component details. See the components are generated for model with abstract big model field test. Before these changes, the result lacked ConcreteBigModel details.
Open API spec that generated without this change:

{
   "openapi":"3.1.0",
   "info":{
      "title":"",
      "version":""
   },
   "paths":{
      "/api/v1/endpoint":{
         "get":{
            "responses":{
               "200":{
                  "content":{
                     "application/json":{
                        "schema":{
                           "$ref":"#/components/schemas/WithGenericPayload"
                        }
                     }
                  }
               }
            }
         }
      }
   },
   "components":{
      "schemas":{
         "AbstractBigModel":{
            "oneOf":[
               {
                  "$ref":"#/components/schemas/ConcreteBigModel"
               }
            ],
            "discriminator":{
               "propertyName":"type",
               "mapping":{
                  "ConcreteBigModel":"#/components/schemas/ConcreteBigModel"
               }
            }
         },
         "ConcreteBigModel":{
            "$ref":"#/components/schemas/ConcreteBigModel"
         },
         "WithGenericPayload":{
            "type":"object",
            "properties":{
               "a":{
                  "$ref":"#/components/schemas/AbstractBigModel"
               }
            },
            "required":[
               "a"
            ]
         }
      }
   }
}

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