Updated Upstream (Bukkit/CraftBukkit/Spigot)

Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing

Please note that this build includes changes to meet upstreams
requirements for nullability annotations. While we aim for a level of
accuracy, these might not be 100% correct, if there are any issues,
please speak to us on discord, or open an issue on the tracker to
discuss.

Bukkit Changes:
9a6a1de3 Remove nullability annotations from enum constructors
3f0591ea SPIGOT-2540: Add nullability annotations to entire Bukkit API

CraftBukkit Changes:
8d8475fc SPIGOT-4666: Force parameter in HumanEntity#sleep
8b1588e2 Fix ExplosionPrimeEvent#setFire not working with EnderCrystals
39a287b7 Don't ignore newlines in PlayerListHeader/Footer

Spigot Changes:
cf694d87 Add nullability annotations

Spigot-API-Patches/0034-Arrow-pickup-rule-API.patch

@@ -1,14 +1,14 @@
-From 14622209c86028ac63d81543497dfa48290ba377 Mon Sep 17 00:00:00 2001
+From 2286649eb07e4a21436f8d660059dd6fa2f47641 Mon Sep 17 00:00:00 2001
 From: Jedediah Smith <jedediah@silencegreys.com>
 Date: Fri, 4 Mar 2016 03:13:18 -0500
 Subject: [PATCH] Arrow pickup rule API
 
 
 diff --git a/src/main/java/org/bukkit/entity/Arrow.java b/src/main/java/org/bukkit/entity/Arrow.java
-index b74d5f9d..99a44006 100644
+index 99f73a2b..b63f2fd9 100644
 --- a/src/main/java/org/bukkit/entity/Arrow.java
 +++ b/src/main/java/org/bukkit/entity/Arrow.java
-@@ -144,4 +144,38 @@ public interface Arrow extends Projectile {
+@@ -149,4 +149,38 @@ public interface Arrow extends Projectile {
      @Override
      Spigot spigot();
      // Spigot end
@@ -48,5 +48,5 @@ index b74d5f9d..99a44006 100644
 +    // Paper end
  }
 -- 
-2.20.1
+2.21.0