Add variant API to MushroomCow

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftMushroomCow.java

@@ -1,5 +1,6 @@
 package org.bukkit.craftbukkit.entity;
 
+import com.google.common.base.Preconditions;
 import net.minecraft.server.EntityMushroomCow;
 import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.entity.EntityType;
@@ -15,11 +16,24 @@ public class CraftMushroomCow extends CraftCow implements MushroomCow {
         return (EntityMushroomCow) entity;
     }
 
+    @Override
+    public Variant getVariant() {
+        return Variant.values()[getHandle().dV().ordinal()];
+    }
+
+    @Override
+    public void setVariant(Variant variant) {
+        Preconditions.checkArgument(variant != null, "variant");
+
+        getHandle().a(EntityMushroomCow.Type.values()[variant.ordinal()]);
+    }
+
     @Override
     public String toString() {
         return "CraftMushroomCow";
     }
 
+    @Override
     public EntityType getType() {
         return EntityType.MUSHROOM_COW;
     }