Fix PetAppearance ID when there's an Alt Style

I don't think this actually affects any clients in practice, but now
that `PetAppearance` can be influenced not just by pet state ID but
also alt style ID, it's no longer correct to just use pet state ID as
the `id` (the default cache key). This could theoretically cause an alt
style to be locally cached as the default appearance of a
species/color/pose.

Instead, we now append an extra string in the case that there's also an
alt style influencing the appearance. This is a bit of a mess, because
I know there's some tooling that's expecting this field to be strictly
the pet state ID, mainly for support/debugging purposes I think? But I
imagine that's not a big deal in practice, and this change should
narrow the scope of a bug like that to just be like, "error: pet state
123-with-alt-style-456 not found" when trying to save a change to it
or something. Good enough!

src/server/types/PetAppearance.js

@@ -73,7 +73,11 @@ const typeDefs = gql`
   }
 
   type PetAppearance @cacheControl(maxAge: ${oneHour}, staleWhileRevalidate: ${oneWeek}) {
+    """
+    NOTE: In the case of an alt style, this won't match petStateId!
+    """
     id: ID!
+
     species: Species!
     color: Color!
     pose: Pose!
@@ -269,6 +273,12 @@ const resolvers = {
   },
 
   PetAppearance: {
+    id: ({ id, altStyleId }) => {
+      if (altStyleId != null) {
+        return `${id}-with-alt-style-${altStyleId}`;
+      }
+      return id;
+    },
     color: async ({ id }, _, { petStateLoader, petTypeLoader }) => {
       const petState = await petStateLoader.load(id);
       const petType = await petTypeLoader.load(petState.petTypeId);