Auto merge of #17028 - bradwerth:innerClone, r=heycam

Stylo: Deep clone ServoStyleSheets.

MozReview-Commit-ID: 6hYIcOa86Y

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https://bugzilla.mozilla.org/show_bug.cgi?id=1339629
https://reviewboard.mozilla.org/r/135314/

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components/style/gecko/generated/bindings.rs

@@ -1736,6 +1736,10 @@ extern "C" {
     pub fn Servo_StyleSheet_GetRules(sheet: RawServoStyleSheetBorrowed)
      -> ServoCssRulesStrong;
 }
+extern "C" {
+    pub fn Servo_StyleSheet_Clone(sheet: RawServoStyleSheetBorrowed)
+     -> RawServoStyleSheetStrong;
+}
 extern "C" {
     pub fn Servo_StyleSet_Init(pres_context: RawGeckoPresContextOwned)
      -> RawServoStyleSetOwned;