Better handling of allOf in request body (#16991)

* better handling of allOf in request body, add tests

* additional checks

* fix description

samples/client/echo_api/java/apache-httpclient/api/openapi.yaml

@@ -421,6 +421,24 @@ paths:
       - body
       x-content-type: application/json
       x-accepts: application/json
+  /echo/body/allOf/Pet:
+    post:
+      description: Test body parameter(s)
+      operationId: test/echo/body/allOf/Pet
+      requestBody:
+        $ref: '#/components/requestBodies/AllOfPet'
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+          description: Successful operation
+      summary: Test body parameter(s)
+      tags:
+      - body
+      x-content-type: application/json
+      x-accepts: application/json
   /echo/body/Pet/response_string:
     post:
       description: Test empty response body
@@ -541,6 +559,13 @@ components:
           schema:
             $ref: '#/components/schemas/Pet'
       description: Pet object that needs to be added to the store
+    AllOfPet:
+      content:
+        application/json:
+          schema:
+            allOf:
+            - $ref: '#/components/schemas/Pet'
+      description: Pet object that needs to be added to the store
     Tag:
       content:
         application/json: