Auto merge of #14471 - heycam:blockification, r=emilio

adjust display style fixup to handle more Gecko cases

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This tweaks the display property fixup we do when restyling to:

* handle the display values that Gecko supports that Servo doesn't
* blockify grid items (like we do flex items)
* skip the fixup for NAC

And while I'm in the area, this sets `nsStyleDisplay::mOriginalDisplay` too.

r? @bholley cc @SimonSapin

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- [ ] These changes fix #__ (github issue number if applicable).

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components/script/layout_wrapper.rs

@@ -477,6 +477,10 @@ impl<'le> TElement for ServoLayoutElement<'le> {
             })
         }
     }
+
+    fn skip_root_and_item_based_display_fixup(&self) -> bool {
+        false
+    }
 }
 
 impl<'le> PartialEq for ServoLayoutElement<'le> {