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/Add-PlayerConnectionCloseEvent.patch

@@ -34,7 +34,7 @@ how PlayerPreLoginEvent interacts with PlayerConnectionCloseEvent
 is undefined.
 
 diff --git a/src/main/java/net/minecraft/server/LoginListener.java b/src/main/java/net/minecraft/server/LoginListener.java
-index ca76f2a3..dfe7a029 100644
+index ca76f2a38..dfe7a029f 100644
 --- a/src/main/java/net/minecraft/server/LoginListener.java
 +++ b/src/main/java/net/minecraft/server/LoginListener.java
 @@ -0,0 +0,0 @@ public class LoginListener implements PacketLoginInListener, ITickable {
@@ -50,7 +50,7 @@ index ca76f2a3..dfe7a029 100644
      private SecretKey loginKey;
      private EntityPlayer l;
 diff --git a/src/main/java/net/minecraft/server/NetworkManager.java b/src/main/java/net/minecraft/server/NetworkManager.java
-index 0b8796d0..55363723 100644
+index 0b8796d0a..553637239 100644
 --- a/src/main/java/net/minecraft/server/NetworkManager.java
 +++ b/src/main/java/net/minecraft/server/NetworkManager.java
 @@ -0,0 +0,0 @@ import io.netty.handler.timeout.TimeoutException;