Updated Upstream (Bukkit/CraftBukkit)

Upstream has released updates that appear 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:
304e83eb PR-1002: Improve documentation and implementation of getMaxStackSize
e8215ea2 SPIGOT-7638: Library loader does not seem to resolve every dependency
79c595c0 SPIGOT-7637: Bad logic in checking nullability of AttributeModifier slots

CraftBukkit Changes:
91b1fc3f1 SPIGOT-7644: Fix ItemMeta#getAsString
4e77a81e1 SPIGOT-7615: PlayerLeashEntityEvent cancelled eats lead
996f660f3 Do not remove leash knot if leasing to an existing leash knot gets cancelled
f70367d42 SPIGOT-7643: Fix inverted leash event cancelled usage and remove leash knot if no entity gets leashed
7ddb48294 SPIGOT-7640: Abnormal jumping height of wind charge
080c8711e SPIGOT-7639: Incoming plugin channels not working
ad549847e Open a direct connection instead of pinging mojang server to check if it is reachable
38e2926c5 SPIGOT-7365: DamageCause blocked by shield should trigger invulnerableTime

patches/server/0124-Properly-fix-item-duplication-bug.patch

@@ -6,10 +6,10 @@ Subject: [PATCH] Properly fix item duplication bug
 Credit to prplz for figuring out the real issue
 
 diff --git a/src/main/java/net/minecraft/server/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
-index 532282ba4432f55596337f7a0898ecc3d5dc2148..82498ec7f0de4c1b82c7882824587ed3ba7fd5d6 100644
+index 1cda7166fe8974f05d20fdbfbced72f101663d56..a5122de4602db3b93a9221e1a9a33bcb73dbe771 100644
 --- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
 +++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
-@@ -2549,7 +2549,7 @@ public class ServerPlayer extends Player {
+@@ -2559,7 +2559,7 @@ public class ServerPlayer extends Player {
  
      @Override
      public boolean isImmobile() {