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/Implement-Player-Client-Options-API.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Implement Player Client Options API
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperSkinParts.java b/src/main/java/com/destroystokyo/paper/PaperSkinParts.java
 new file mode 100644
-index 0000000000..b6f4400df3
+index 00000000000..b6f4400df3d
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/PaperSkinParts.java
 @@ -0,0 +0,0 @@
@@ -85,7 +85,7 @@ index 0000000000..b6f4400df3
 +    }
 +}
 diff --git a/src/main/java/net/minecraft/server/EntityHuman.java b/src/main/java/net/minecraft/server/EntityHuman.java
-index c4d4334305..7df24be46e 100644
+index c4d43343050..7df24be46e4 100644
 --- a/src/main/java/net/minecraft/server/EntityHuman.java
 +++ b/src/main/java/net/minecraft/server/EntityHuman.java
 @@ -0,0 +0,0 @@ public abstract class EntityHuman extends EntityLiving {
@@ -98,7 +98,7 @@ index c4d4334305..7df24be46e 100644
      protected static final DataWatcherObject<NBTTagCompound> bs = DataWatcher.a(EntityHuman.class, DataWatcherRegistry.p);
      protected static final DataWatcherObject<NBTTagCompound> bt = DataWatcher.a(EntityHuman.class, DataWatcherRegistry.p);
 diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
-index f453ccdb02..bf2ba0548d 100644
+index f453ccdb020..bf2ba0548d9 100644
 --- a/src/main/java/net/minecraft/server/EntityPlayer.java
 +++ b/src/main/java/net/minecraft/server/EntityPlayer.java
 @@ -0,0 +0,0 @@ package net.minecraft.server;
@@ -127,7 +127,7 @@ index f453ccdb02..bf2ba0548d 100644
          if (getMainHand() != packetplayinsettings.getMainHand()) {
              PlayerChangedMainHandEvent event = new PlayerChangedMainHandEvent(getBukkitEntity(), getMainHand() == EnumMainHand.LEFT ? MainHand.LEFT : MainHand.RIGHT);
 diff --git a/src/main/java/net/minecraft/server/PacketPlayInSettings.java b/src/main/java/net/minecraft/server/PacketPlayInSettings.java
-index 8faebf9efe..4da6371381 100644
+index 8faebf9efed..4da63713819 100644
 --- a/src/main/java/net/minecraft/server/PacketPlayInSettings.java
 +++ b/src/main/java/net/minecraft/server/PacketPlayInSettings.java
 @@ -0,0 +0,0 @@ public class PacketPlayInSettings implements Packet<PacketListenerPlayIn> {
@@ -154,7 +154,7 @@ index 8faebf9efe..4da6371381 100644
          return this.e;
      }
 diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-index 6672feaf51..dcbda5b35a 100644
+index 6672feaf519..dcbda5b35ab 100644
 --- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
 +++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
 @@ -0,0 +0,0 @@