Optimize Network Manager to not need synchronization

Removes synchronization from sending packets
Makes normal packet sends no longer need to be wrapped and queued like it use to work.
Adds more packet queue immunities on top of keep alive to let the following scenarios go out
without delay:
  - Keep Alive
  - Chat
  - Kick
  - All of the packets during the Player Joined World event

Hoping that latter one helps join timeout issues more too for slow connections.

Removes processing packet queue off of main thread
  - for the few cases where it is allowed, order is not necessary nor
    should it even be happening concurrently in first place (handshaking/login/status)

Ensures packets sent asynchronously are dispatched on main thread

This helps ensure safety for ProtocolLib as packet listeners
are commonly accessing world state. This will allow you to schedule
a packet to be sent async, but itll be dispatched sync for packet
listeners to process.

This should solve some deadlock risks

This may provide a decent performance improvement because thread synchronization incurs a cache reset
so by avoiding ever entering a synchronized block, we get to avoid that, and packet sending is a really
hot activity.

Spigot-Server-Patches/Fix-Longstanding-Broken-behavior-of-PlayerJoinEvent.patch

@@ -28,7 +28,7 @@ receives a deterministic result, and should no longer require 1 tick
 delays anymore.
 
 diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
-index bf2ba0548d..45df816980 100644
+index bf2ba0548d9..45df816980c 100644
 --- a/src/main/java/net/minecraft/server/EntityPlayer.java
 +++ b/src/main/java/net/minecraft/server/EntityPlayer.java
 @@ -0,0 +0,0 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
@@ -40,7 +40,7 @@ index bf2ba0548d..45df816980 100644
      // CraftBukkit end
      public PlayerNaturallySpawnCreaturesEvent playerNaturallySpawnedEvent; // Paper
 diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
-index cc400a9a84..a06c0327df 100644
+index 79133dd40c4..ea0086ceb64 100644
 --- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
 +++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
 @@ -0,0 +0,0 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
@@ -52,7 +52,7 @@ index cc400a9a84..a06c0327df 100644
          if (!(entity instanceof EntityComplexPart)) {
              if (!(entity instanceof EntityLightning)) {
 diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
-index 7403be0b25..ec45c30dd3 100644
+index e79a4d9ff80..6a4e4f93eb3 100644
 --- a/src/main/java/net/minecraft/server/PlayerList.java
 +++ b/src/main/java/net/minecraft/server/PlayerList.java
 @@ -0,0 +0,0 @@ public abstract class PlayerList {