LibWeb: Implement faster equals() for UnresolvedStyleValue

Compare `Vector<Parser::ComponentValue>` directly instead of
serializing them into strings first.

This is required for the upcoming changes where we would compare
previous and new sets of custom properties to figure out whether we need
to invalidate descendant elements. Without this change `equals()` would
show up being hot in profiles.

Libraries/LibWeb/CSS/StyleValues/UnresolvedStyleValue.cpp

@@ -48,8 +48,7 @@ bool UnresolvedStyleValue::equals(CSSStyleValue const& other) const
 {
     if (type() != other.type())
         return false;
-    // This is a case where comparing the strings actually makes sense.
-    return to_string(SerializationMode::Normal) == other.to_string(SerializationMode::Normal);
+    return values() == other.as_unresolved().values();
 }
 
 }