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/api/0349-Add-enchantWithLevels-API.patch

@@ -70,10 +70,10 @@ index dbebaf8172ec6872f56958b9583affde4f8400a4..98a970a6582dca22e719a31559c7bece
 +    // Paper end - enchantWithLevels API
  }
 diff --git a/src/main/java/org/bukkit/inventory/ItemStack.java b/src/main/java/org/bukkit/inventory/ItemStack.java
-index 455e633edc19d29559e66b1d52c532ef1a0fa8df..637b9067973aadece2806cc2b6200a4d3b8d97a1 100644
+index 351f5c0feec38377fccf09bfc1cef2df88fc2dcd..7eb4cf0b2f162d650252d81e9d38393f69a69046 100644
 --- a/src/main/java/org/bukkit/inventory/ItemStack.java
 +++ b/src/main/java/org/bukkit/inventory/ItemStack.java
-@@ -667,6 +667,24 @@ public class ItemStack implements Cloneable, ConfigurationSerializable, Translat
+@@ -670,6 +670,24 @@ public class ItemStack implements Cloneable, ConfigurationSerializable, Translat
      }
  
      // Paper start