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/Expose-attack-cooldown-methods-for-Player.patch

@@ -1,38 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: BillyGalbreath <Blake.Galbreath@GMail.com>
-Date: Tue, 4 Sep 2018 15:01:54 -0500
-Subject: [PATCH] Expose attack cooldown methods for Player
-
-
-diff --git a/src/main/java/org/bukkit/entity/Player.java b/src/main/java/org/bukkit/entity/Player.java
-index ddf226a4..db6bcae5 100644
---- a/src/main/java/org/bukkit/entity/Player.java
-+++ b/src/main/java/org/bukkit/entity/Player.java
-@@ -0,0 +0,0 @@ public interface Player extends HumanEntity, Conversable, OfflinePlayer, PluginM
-      * @param profile The new profile to use
-      */
-     void setPlayerProfile(PlayerProfile profile);
-+
-+    /**
-+     * Returns the amount of ticks the current cooldown lasts
-+     *
-+     * @return Amount of ticks cooldown will last
-+     */
-+    float getCooldownPeriod();
-+
-+    /**
-+     * Returns the percentage of attack power available based on the cooldown (zero to one).
-+     *
-+     * @param adjustTicks Amount of ticks to add to cooldown counter for this calculation
-+     * @return Percentage of attack power available
-+     */
-+    float getCooledAttackStrength(float adjustTicks);
-+
-+    /**
-+     * Reset the cooldown counter to 0, effectively starting the cooldown period.
-+     */
-+    void resetCooldown();
-     // Paper end
- 
-     // Spigot start
---