LibWeb: Rename CSS::StyleProperties => CSS::ComputedProperties

Now that StyleProperties is only used to hold computed properties, let's
name it ComputedProperties.

Libraries/LibWeb/DOM/Document.cpp

@@ -1386,7 +1386,7 @@ void Document::update_animated_style_if_needed()
 
         for (auto& animation : timeline->associated_animations()) {
             if (auto effect = animation->effect())
-                effect->update_style_properties();
+                effect->update_computed_properties();
         }
     }
     m_needs_animated_style_update = false;