Fix CME in StructureTemplate.Palette

The cache needs to be a CHM to prevent CMEs. Since the only usage
is compute() on static data, this is all we need to fix the
threading issues here.

src/main/java/ca/spottedleaf/moonrise/mixin/chunk_system/StructureTemplate$PaletteMixin.java

@@ -0,0 +1,35 @@
+package ca.spottedleaf.moonrise.mixin.chunk_system;
+
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplate;
+import org.objectweb.asm.Opcodes;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.Redirect;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+@Mixin(StructureTemplate.Palette.class)
+public abstract class StructureTemplate$PaletteMixin {
+
+    @Shadow
+    private Map<Block, List<StructureTemplate.StructureBlockInfo>> cache;
+
+    /**
+     * @reason Make cache CHM to prevent CME
+     * @author Spottedleaf
+     */
+    @Inject(
+            method = "<init>",
+            at = @At(
+                    value = "RETURN"
+            )
+    )
+    private <K, V> void makeCacheCHM(final CallbackInfo ci) {
+        this.cache = new ConcurrentHashMap<>();
+    }
+}

src/main/resources/moonrise.accesswidener

@@ -253,4 +253,8 @@ mutable field net/minecraft/client/multiplayer/ClientLevel entityStorage Lnet/mi
 
 # ClientLevel$EntityCallbacks
 accessible class net/minecraft/client/multiplayer/ClientLevel$EntityCallbacks
-accessible method net/minecraft/client/multiplayer/ClientLevel$EntityCallbacks <init> (Lnet/minecraft/client/multiplayer/ClientLevel;)V
+accessible method net/minecraft/client/multiplayer/ClientLevel$EntityCallbacks <init> (Lnet/minecraft/client/multiplayer/ClientLevel;)V
+
+
+# StructureTemplate$Palette
+mutable field net/minecraft/world/level/levelgen/structure/templatesystem/StructureTemplate$Palette cache Ljava/util/Map;

src/main/resources/moonrise.mixins.json

@@ -43,6 +43,7 @@
     "chunk_system.ServerPlayerMixin",
     "chunk_system.SortedArraySetMixin",
     "chunk_system.StructureCheckMixin",
+    "chunk_system.StructureTemplate$PaletteMixin",
     "chunk_system.TicketMixin",
     "collisions.ArmorStandMixin",
     "collisions.ArrayVoxelShapeMixin",