Auto merge of #19038 - CJ8664:master, r=jdm

Added implementation for itemprop and itemtype along with test files

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

<!-- Either: -->
- [x] There are tests for these changes OR

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/19038)
<!-- Reviewable:end -->

components/script/dom/webidls/HTMLElement.webidl

@@ -18,9 +18,14 @@ interface HTMLElement : Element {
 
   // microdata
   //         attribute boolean itemScope;
+
   //         attribute DOMString itemId;
   //readonly attribute HTMLPropertiesCollection properties;
   //         attribute any itemValue; // acts as DOMString on setting
+  [Pref="dom.microdata.testing.enabled"]
+  sequence<DOMString>? propertyNames();
+  [Pref="dom.microdata.testing.enabled"]
+  sequence<DOMString>? itemtypes();
 
   // user interaction
   [CEReactions]