stylo: Do not skip parent display-based style fixups for NAC that is …

…not a NAC root

Stylo is currently skipping parent display-based style fixups for all NAC,
whereas we probably only want to do this for NAC roots.

In this patch, we ensure that we skip it for NAC roots, and pseudo-elements,
but not other NAC.

components/style/gecko/wrapper.rs

@@ -1171,7 +1171,9 @@ impl<'le> TElement for GeckoElement<'le> {
         // level native anonymous content subtree roots, since they're not
         // really roots from the style fixup perspective.  Checking that we
         // are NAC handles both cases.
-        self.is_native_anonymous()
+        self.is_native_anonymous() &&
+        (self.is_root_of_native_anonymous_subtree() ||
+         self.implemented_pseudo_element().is_some())
     }
 
     unsafe fn set_selector_flags(&self, flags: ElementSelectorFlags) {