Add API to manipulate boss bar of entities and those created by commands

By: Yannick Lamprecht <yannicklamprecht@live.de>

paper-server/nms-patches/EntityWither.patch

@@ -13,6 +13,15 @@
  public class EntityWither extends EntityMonster implements IRangedEntity {
  
      private static final DataWatcherObject<Integer> a = DataWatcher.a(EntityWither.class, DataWatcherRegistry.b);
+@@ -19,7 +25,7 @@
+     private final int[] bI = new int[2];
+     private final int[] bJ = new int[2];
+     private int bK;
+-    private final BossBattleServer bL;
++    public final BossBattleServer bL; // PAIL private -> public, rename bossBattleServer
+     private static final Predicate<Entity> bM = (entity) -> {
+         return entity instanceof EntityLiving && ((EntityLiving) entity).getMonsterType() != EnumMonsterType.UNDEAD && ((EntityLiving) entity).df();
+     };
 @@ -181,13 +187,38 @@
          if (this.dz() > 0) {
              i = this.dz() - 1;