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-Server-Patches/Configurable-connection-throttle-kick-message.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Configurable connection throttle kick message
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
-index 94252008..7f9845d9 100644
+index 942520088..7f9845d92 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 @@ -0,0 +0,0 @@ public class PaperConfig {
@@ -21,7 +21,7 @@ index 94252008..7f9845d9 100644
      private static void savePlayerData() {
          savePlayerData = getBoolean("settings.save-player-data", savePlayerData);
 diff --git a/src/main/java/net/minecraft/server/HandshakeListener.java b/src/main/java/net/minecraft/server/HandshakeListener.java
-index e732d55f..2c594b43 100644
+index e732d55f9..2c594b437 100644
 --- a/src/main/java/net/minecraft/server/HandshakeListener.java
 +++ b/src/main/java/net/minecraft/server/HandshakeListener.java
 @@ -0,0 +0,0 @@ public class HandshakeListener implements PacketHandshakingInListener {