Auto merge of #12924 - servo:selectors-ser, r=nox

Update selectors to 0.10, with ToCss serialization.

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r? @emilio

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ports/geckolib/wrapper.rs

@@ -587,7 +587,7 @@ impl AttrSelectorHelpers for AttrSelector<GeckoSelectorImpl> {
     fn ns_or_null(&self) -> *mut nsIAtom {
         match self.namespace {
             NamespaceConstraint::Any => ptr::null_mut(),
-            NamespaceConstraint::Specific(ref ns) => ns.0.as_ptr(),
+            NamespaceConstraint::Specific(ref ns) => ns.url.0.as_ptr(),
         }
     }