Implement Gecko_StyleAnimationsEquals for checking nsStyleAutoArray<StyleAnimation> equality in servo side.

Later we update CSS animations if this function returns false.

components/style/properties/gecko.mako.rs

@@ -1801,6 +1801,10 @@ fn static_assert() {
     }
     ${impl_transition_count('property', 'Property')}
 
+    pub fn animations_equals(&self, other: &Self) -> bool {
+        unsafe { bindings::Gecko_StyleAnimationsEquals(&self.gecko.mAnimations, &other.gecko.mAnimations) }
+    }
+
     pub fn set_animation_name(&mut self, v: longhands::animation_name::computed_value::T) {
         use nsstring::nsCString;