Add cancellability to PlayerTrackEntityEvent (#8605)

patches/api/Player-Entity-Tracking-Events.patch

@@ -14,17 +14,21 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +import org.bukkit.entity.Entity;
 +import org.bukkit.entity.Player;
++import org.bukkit.event.Cancellable;
 +import org.bukkit.event.HandlerList;
 +import org.bukkit.event.player.PlayerEvent;
 +import org.jetbrains.annotations.NotNull;
 +
 +/**
 + * Is called when a {@link Player} tracks an {@link Entity}.
++ * <p>
++ * If cancelled entity is not shown to the player and interaction in both directions is not possible.
 + */
-+public class PlayerTrackEntityEvent extends PlayerEvent {
++public class PlayerTrackEntityEvent extends PlayerEvent implements Cancellable {
 +
 +    private static final HandlerList handlers = new HandlerList();
 +    private final Entity entity;
++    private boolean cancelled;
 +
 +    public PlayerTrackEntityEvent(@NotNull Player player, @NotNull Entity entity) {
 +        super(player);
@@ -51,6 +55,16 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    public Entity getEntity() {
 +        return entity;
 +    }
++
++    @Override
++    public boolean isCancelled() {
++        return cancelled;
++    }
++
++    @Override
++    public void setCancelled(boolean cancel) {
++        this.cancelled = cancel;
++    }
 +}
 diff --git a/src/main/java/io/papermc/paper/event/player/PlayerUntrackEntityEvent.java b/src/main/java/io/papermc/paper/event/player/PlayerUntrackEntityEvent.java
 new file mode 100644