Switch to using ForgeFlower for Paper Only mc-dev imports

ForgeFlower is better than Spigots FernFlower at decompiling the source.

However, in order to maintain the CraftBukkit patches, we must keep
using spigots for the primary.

However, for any file that we import on top of Spigots imported files
there is nothing stopping us from using better decompiled files.

So these changes will use ForgeFlower to maintain a better set of
decomped files, so anything we add on top of Paper can start off
in a better spot.

Spigot-Server-Patches/SkeletonHorse-Additions.patch

@@ -5,11 +5,11 @@ Subject: [PATCH] SkeletonHorse Additions
 
 
 diff --git a/src/main/java/net/minecraft/server/EntityHorseSkeleton.java b/src/main/java/net/minecraft/server/EntityHorseSkeleton.java
-index e643201ebf..edd272eabd 100644
+index e3690db471..ba6c0e96a3 100644
 --- a/src/main/java/net/minecraft/server/EntityHorseSkeleton.java
 +++ b/src/main/java/net/minecraft/server/EntityHorseSkeleton.java
-@@ -0,0 +0,0 @@ public class EntityHorseSkeleton extends EntityHorseAbstract {
- 
+@@ -0,0 +0,0 @@ import javax.annotation.Nullable;
+ public class EntityHorseSkeleton extends EntityHorseAbstract {
      private final PathfinderGoalHorseTrap bM = new PathfinderGoalHorseTrap(this);
      private boolean bN;
 -    private int bO;