feat(RequestBody): validation support for required fields (#6223)

fixes #5181

* application/json
* application/xml
* application/x-www-form-urlencoded

* Set requestBodyValue values to be an immutable Map, as "value". Previously stored as a normal String.
* This enables adding "errors" to the Map, for validation use

* note: getOAS3RequiredRequestBodyContentType requires state.spec,
* which is not available to state.oas3

test/e2e-cypress/static/documents/bugs/5181.yaml

@@ -0,0 +1,27 @@
+info:
+  title: Required parameter missing, doesn't block request from executing.
+  version: '1'
+openapi: 3.0.0
+servers: 
+- url: http://httpbin.org/anything
+paths:
+  /foos:
+    post:
+      requestBody:
+        content:
+          application/x-www-form-urlencoded:
+          # application/json:
+          # application/xml:
+            schema:
+              properties:
+                foo:
+                  type: string
+                bar:
+                  type: string
+              required:
+                - foo
+              type: object
+        required: true # Note this doesn't have an impact
+      responses:
+        default:
+          description: ok

test/e2e-cypress/static/documents/features/petstore-only-pet.openapi.yaml

@@ -415,4 +415,4 @@ components:
     api_key:
       type: apiKey
       name: api_key
-      in: header
+      in: header