Add Velocity IP forwarding support (#1557)

While Velocity supports BungeeCord-style IP forwarding, it is not secure. Users
have a lot of problems setting up firewalls or setting up plugins like IPWhitelist.
Further, the BungeeCord IP forwarding protocol still retains essentially its original
form, when there is brand new support for custom login plugin messages in 1.13.

Velocity's modern IP forwarding uses an HMAC-SHA256 code to ensure authenticity
of messages, is packed into a binary format that is smaller than BungeeCord's
forwarding, and is integrated into the Minecraft login process by using the 1.13
login plugin message packet.

Spigot-Server-Patches/Auto-Save-Improvements.patch

@@ -12,7 +12,7 @@ Re-introduce a cap per tick for auto save (Spigot disabled the vanilla cap) and
 Adds incremental player auto saving too
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
-index 44d8e99ff8..b9acfaf51b 100644
+index c278ac98d..ae3d0f8f7 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 @@ -0,0 +0,0 @@ public class PaperConfig {
@@ -32,7 +32,7 @@ index 44d8e99ff8..b9acfaf51b 100644
 +    }
  }
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 0cd15c17e8..c43152f456 100644
+index 0cd15c17e..c43152f45 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@ package com.destroystokyo.paper;
@@ -64,7 +64,7 @@ index 0cd15c17e8..c43152f456 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
-index 7e371c278f..a79b0b59d7 100644
+index 7e371c278..a79b0b59d 100644
 --- a/src/main/java/net/minecraft/server/Chunk.java
 +++ b/src/main/java/net/minecraft/server/Chunk.java
 @@ -0,0 +0,0 @@ public class Chunk implements IChunkAccess {
@@ -96,7 +96,7 @@ index 7e371c278f..a79b0b59d7 100644
  
      public boolean isEmpty() {
 diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
-index 719d5deb2c..69219b13a6 100644
+index 719d5deb2..69219b13a 100644
 --- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
 +++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
 @@ -0,0 +0,0 @@ public class ChunkProviderServer implements IChunkProvider {
@@ -109,7 +109,7 @@ index 719d5deb2c..69219b13a6 100644
                      }
                  }
 diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
-index 3d83900298..690cff8828 100644
+index 3d8390029..690cff882 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 {
@@ -121,7 +121,7 @@ index 3d83900298..690cff8828 100644
      public final MinecraftServer server;
      public final PlayerInteractManager playerInteractManager;
 diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
-index 04d8c108b4..a547ee5ca1 100644
+index 04d8c108b..a547ee5ca 100644
 --- a/src/main/java/net/minecraft/server/MinecraftServer.java
 +++ b/src/main/java/net/minecraft/server/MinecraftServer.java
 @@ -0,0 +0,0 @@ public abstract class MinecraftServer implements IAsyncTaskHandler, IMojangStati
@@ -168,7 +168,7 @@ index 04d8c108b4..a547ee5ca1 100644
          this.methodProfiler.a("snooper");
          if (getSnooperEnabled() && !this.i.d() && this.ticks > 100) { // Spigot
 diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
-index baf870ac2a..7d778ff3e0 100644
+index baf870ac2..7d778ff3e 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 {
@@ -207,7 +207,7 @@ index baf870ac2a..7d778ff3e0 100644
      public WhiteList getWhitelist() {
          return this.whitelist;
 diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
-index c5201697d5..ca2e027cda 100644
+index c5201697d..ca2e027cd 100644
 --- a/src/main/java/net/minecraft/server/WorldServer.java
 +++ b/src/main/java/net/minecraft/server/WorldServer.java
 @@ -0,0 +0,0 @@ public class WorldServer extends World implements IAsyncTaskHandler {