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

By: Yannick Lamprecht <yannicklamprecht@live.de>

paper-server/nms-patches/BossBattleCustom.patch

@@ -0,0 +1,30 @@
+--- a/net/minecraft/server/BossBattleCustom.java
++++ b/net/minecraft/server/BossBattleCustom.java
+@@ -8,12 +8,27 @@
+ import java.util.UUID;
+ import java.util.function.Consumer;
+ 
++// CraftBukkit start
++import org.bukkit.boss.KeyedBossBar;
++import org.bukkit.craftbukkit.boss.CraftKeyedBossbar;
++// CraftBukkit end
++
+ public class BossBattleCustom extends BossBattleServer {
+ 
+     private final MinecraftKey h;
+     private final Set<UUID> i = Sets.newHashSet();
+     private int j;
+     private int k = 100;
++    // CraftBukkit start
++    private KeyedBossBar bossBar;
++
++    public KeyedBossBar getBukkitEntity() {
++        if (bossBar == null) {
++            bossBar = new CraftKeyedBossbar(this);
++        }
++        return bossBar;
++    }
++    // CraftBukkit end
+ 
+     public BossBattleCustom(MinecraftKey minecraftkey, IChatBaseComponent ichatbasecomponent) {
+         super(ichatbasecomponent, BossBattle.BarColor.WHITE, BossBattle.BarStyle.PROGRESS);

paper-server/nms-patches/EnderDragonBattle.patch

@@ -0,0 +1,11 @@
+--- a/net/minecraft/server/EnderDragonBattle.java
++++ b/net/minecraft/server/EnderDragonBattle.java
+@@ -21,7 +21,7 @@
+ 
+     private static final Logger a = LogManager.getLogger();
+     private static final Predicate<Entity> b = IEntitySelector.a.and(IEntitySelector.a(0.0D, 128.0D, 0.0D, 192.0D));
+-    private final BossBattleServer c;
++    public final BossBattleServer c; // PAIL private -> public, rename bossBattleServer
+     private final WorldServer d;
+     private final List<Integer> e;
+     private final ShapeDetector f;

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;