Fix crash when generating swamp structure

Need to implement structureManager on CB's DelegatedGeneratorAccess,
as that is now used during population.

patches/server/0003-Threaded-Regions.patch

@@ -22583,6 +22583,24 @@ index 96f6e0554baf5915dd1f5b93f3bcfe7a13393c29..17c5ef57bed41fca97b845f1f6d1752a
          if (pdf.getAPIVersion() != null) {
              int pluginIndex = CraftMagicNumbers.SUPPORTED_API.indexOf(pdf.getAPIVersion());
 
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/DelegatedGeneratorAccess.java b/src/main/java/org/bukkit/craftbukkit/util/DelegatedGeneratorAccess.java
+index cbedb6f002bc01daa16d349421c4ef04d4bcbcb2..2d708bb11f841bb265d12a025dbaa657b0b4d08a 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/DelegatedGeneratorAccess.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/DelegatedGeneratorAccess.java
+@@ -69,6 +69,13 @@ public abstract class DelegatedGeneratorAccess implements WorldGenLevel {
+         this.handle = worldAccess;
+     }
+
++    // Folia start - region threading
++    @Override
++    public net.minecraft.world.level.StructureManager structureManager() {
++        return this.handle.structureManager();
++    }
++    // Folia end - region threading
++
+     public WorldGenLevel getHandle() {
+         return this.handle;
+     }
 diff --git a/src/main/java/org/spigotmc/ActivationRange.java b/src/main/java/org/spigotmc/ActivationRange.java
 index 2f9e5a1adf9d67ffe18d95f2822ca3d2288fb27a..23ec7dd6fe49f33e9cac78fd084dc660fc5a2b2e 100644
 --- a/src/main/java/org/spigotmc/ActivationRange.java