Updated Upstream (Bukkit/CraftBukkit)

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

Bukkit Changes:
18cda936 Fix variant of unloadChunkRequest that was incorrectly never deprecated
00763e1b Deprecate some methods
35a83d54 SPIGOT-4572: Make default no permission message clearer
6163343d Fix some misplaced material enum entries
8736469c Fix typo in TechnicalPiston documentation

CraftBukkit Changes:
0c715b32 SPIGOT-4579: Shulker boxes not dropping in creative
50fbc3f1 SPIGOT-4576: Fix attributes in itemstack internal data being lost
8059a937 SPIGOT-4577: Fix loss of int/double custom tags when serialized to yaml
07e504c3 Clarify exception thrown when setting drop chance for player inventory
98b862ad Fix duplicate iron golem add
843cee65 Fix a bunch of duplicate EntityCombustEvent calls
43855624 SPIGOT-4571: EntityCombustEvent not firing for phantoms

Spigot-Server-Patches/PlayerReadyArrowEvent.patch

@@ -7,16 +7,17 @@ Called when a player is firing a bow and the server is choosing an arrow to use.
 Plugins can skip selection of certain arrows and control which is used.
 
 diff --git a/src/main/java/net/minecraft/server/ItemBow.java b/src/main/java/net/minecraft/server/ItemBow.java
-index 1eadc4371..80f112d99 100644
+index 52bc68e6a6..f8dbc3c400 100644
 --- a/src/main/java/net/minecraft/server/ItemBow.java
 +++ b/src/main/java/net/minecraft/server/ItemBow.java
 @@ -0,0 +0,0 @@
  package net.minecraft.server;
  
 +import org.bukkit.craftbukkit.inventory.CraftItemStack;
- import org.bukkit.event.entity.EntityCombustEvent; // CraftBukkit
- 
++
  public class ItemBow extends Item {
+ 
+     public ItemBow(Item.Info item_info) {
 @@ -0,0 +0,0 @@ public class ItemBow extends Item {
          // CraftBukkit end
      }