Restore single type entity ingredient syntax

Same deal as fluid ingredient, help other mods that relied on teh old syntax, though in this case no need to deprecate it. Might want a more general way to do a list or value type field in the future

src/main/java/slimeknights/mantle/recipe/ingredient/EntityIngredient.java

@@ -31,8 +31,16 @@ public abstract class EntityIngredient implements Predicate<EntityType<?>>, IAmL
 
   /** Creates a builder with set and tag */
   private static EitherLoadable.TypedBuilder<EntityIngredient> loadableBuilder() {
-    return EitherLoadable.<EntityIngredient>typed().key("types", SET_MATCH).key("tag", TAG_MATCH);
+    return EitherLoadable.<EntityIngredient>typed().key("types", SET_MATCH).key("type", ENTRY_MATCH).key("tag", TAG_MATCH);
   }
+  /** Loadable for a single value, notably not used for networking (though that probably would still work fine due to how EitherLoadable works) */
+  private static final RecordLoadable<EntityIngredient> ENTRY_MATCH = RecordLoadable.create(Loadables.ENTITY_TYPE.requiredField("type", i -> {
+    Set<EntityType<?>> types = i.getTypes();
+    if (types.size() == 1) {
+      return types.iterator().next();
+    }
+    throw new IllegalStateException("Cannot use entry match to serialize more than 1 entity");
+  }), EntityIngredient::of);
   /** Loadable for a set match */
   private static final RecordLoadable<EntityIngredient> SET_MATCH = RecordLoadable.create(Loadables.ENTITY_TYPE.set().requiredField("types", EntityIngredient::getTypes), EntityIngredient::of);
   /** Loadable for a tag match */
@@ -122,7 +130,7 @@ private static class SetMatch extends EntityIngredient {
 
     @Override
     public Loadable<?> loadable() {
-      return SET_MATCH;
+      return types.size() == 1 ? ENTRY_MATCH : SET_MATCH;
     }
 
     @Override