SPIGOT-7732, SPIGOT-7786: Add freezing damage modifier

By: LoliColleen <76620594+LoliColleen@users.noreply.github.com>

paper-api/src/main/java/org/bukkit/event/entity/EntityDamageEvent.java

@@ -247,6 +247,10 @@ public class EntityDamageEvent extends EntityEvent implements Cancellable {
          * raw {@link EntityDamageEvent#getDamage()}.
          */
         BASE,
+        /**
+         * This represents the damage increased by freezing status.
+         */
+        FREEZING,
         /**
          * This represents the damage reduced by a wearing a helmet when hit
          * by a falling block.