Fix setting difficulity inside of API (Fixes #8533)

Vanilla moved some logic around setting the world difficulty which
was not adopted for inside of upstream properly, this addresses another
such case

patches/server/Fix-Per-World-Difficulty-Remembering-Difficulty.patch

@@ -116,3 +116,16 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
  
              for (SpawnCategory spawnCategory : SpawnCategory.values()) {
                  if (CraftSpawnCategory.isValidForLimits(spawnCategory)) {
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+@@ -0,0 +0,0 @@ public class CraftWorld extends CraftRegionAccessor implements World {
+ 
+     @Override
+     public void setDifficulty(Difficulty difficulty) {
+-        this.getHandle().serverLevelData.setDifficulty(net.minecraft.world.Difficulty.byId(difficulty.getValue()));
++        this.getHandle().getServer().setDifficulty(this.getHandle(), net.minecraft.world.Difficulty.byId(difficulty.getValue()), true); // Paper - don't skip other difficulty-changing logic
+     }
+ 
+     @Override