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

Added implementation for itemprop and itemtype along with test files

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resources/prefs.json

@@ -6,6 +6,7 @@
   "dom.customelements.enabled": true,
   "dom.forcetouch.enabled": false,
   "dom.gamepad.enabled": false,
+  "dom.microdata.testing.enabled": true,
   "dom.mouseevent.which.enabled": false,
   "dom.mozbrowser.enabled": false,
   "dom.mutation_observer.enabled": false,