fix(sample-gen): first oneOf or anyOf should be combined with schema (#6775)

* fix(sample-gen): oneOf and anyOf should be merge into schema

when there was oneOf or anyOf defined it just used the first schema of it to generate the samples.
Now, the first oneOf or anyOf is combined with the schema to generate samples.

* test(sample-gen): oneOf and anyOf should be combined with schema

test/unit/core/plugins/samples/fn.js

@@ -29,6 +29,72 @@ describe("sampleFromSchema", () => {
     expect(sampleFromSchema(definition, { includeReadOnly: false })).toEqual(expected)
   })
 
+  it("combine first oneOf or anyOf with schema's definitions", function () {
+    let definition = {
+      type: "object",
+      anyOf: [
+        {
+          type: "object",
+          properties: {
+            test2: {
+              type: "string",
+              example: "anyOf"
+            },
+            test: {
+              type: "string",
+              example: "anyOf"
+            }
+          }
+        }
+      ],
+      properties: {
+        test: {
+          type: "string",
+          example: "schema"
+        }
+      }
+    }
+
+    let expected = {
+      test: "schema",
+      test2: "anyOf"
+    }
+
+    expect(sampleFromSchema(definition, { includeReadOnly: false })).toEqual(expected)
+
+    definition = {
+      type: "object",
+      oneOf: [
+        {
+          type: "object",
+          properties: {
+            test2: {
+              type: "string",
+              example: "oneOf"
+            },
+            test: {
+              type: "string",
+              example: "oneOf"
+            }
+          }
+        }
+      ],
+      properties: {
+        test: {
+          type: "string",
+          example: "schema"
+        }
+      }
+    }
+
+    expected = {
+      test: "schema",
+      test2: "oneOf"
+    }
+
+    expect(sampleFromSchema(definition, { includeReadOnly: false })).toEqual(expected)
+  })
+
   it("returns object with no readonly fields for parameter", function () {
     let definition = {
       type: "object",