fix(schema example): xml gen should follow json gen behavior (#6555)

* ref: #6470 
* fixes: #6540
* fixes: #4943 

* add example override option to json
* add example override option to xml
* added basic oneOf and anyOf support
* fix anyof|oneof
* only lift xml to items


Co-authored-by: Tim Lai <timothy.lai@gmail.com>

test/e2e-cypress/tests/bugs/4943.js

@@ -0,0 +1,20 @@
+describe("#4943: XML example not rendered correctly with oneOf", () => {
+  it("should render integer property correctly", () => {
+    cy
+      .visit("/?url=/documents/bugs/4943.yaml")
+      .get("#operations-Test-postTest")
+      .click()
+      .get(".microlight")
+      .contains("<b>0</b>")
+  })
+  it("should render oneOf property correctly", () => {
+    cy
+      .visit("/?url=/documents/bugs/4943.yaml")
+      .get("#operations-Test-postTest")
+      .click()
+      .get(".try-out__btn")
+      .click()
+      .get(".microlight")
+      .contains("<c>\n\t</c>")
+  })
+})

test/e2e-cypress/tests/bugs/6540.js

@@ -0,0 +1,11 @@
+describe("#6540: XML example not rendered correctly with oneOf", () => {
+  it("should render xml like json", () => {
+    const expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<test>\n\t<a>string</a>\n\t<b>0</b>\n\t<c>\n\t\t<ObjectType>Text</ObjectType>\n\t\t<Data>This is a text</Data>\n\t</c>\n\t<c>\n\t\t<ObjectType>image</ObjectType>\n\t\t<Data>This is a image</Data>\n\t</c>\n\t<d>\n\t\t<ObjectType>Text</ObjectType>\n\t\t<Data>This is a text</Data>\n\t</d>\n\t<d>\n\t\t<ObjectType>image</ObjectType>\n\t\t<Data>This is a image</Data>\n\t</d>\n</test>"
+    cy
+      .visit("/?url=/documents/bugs/6540.yaml")
+      .get("#operations-Test-postTest")
+      .click()
+      .get(".microlight")
+      .contains(expected)
+  })
+})