Add remapping chain -> iron_chaion for RP version 67 and above for backwards compatibillity

Author: TBlueF

core/src/main/resourceExtensions/mc1_21_9/assets/minecraft/blockstates/chain.json

@@ -0,0 +1,16 @@
+{
+  "variants": {
+    "axis=x": {
+      "model": "minecraft:block/iron_chain",
+      "x": 90,
+      "y": 90
+    },
+    "axis=y": {
+      "model": "minecraft:block/iron_chain"
+    },
+    "axis=z": {
+      "model": "minecraft:block/iron_chain",
+      "x": 90
+    }
+  }
+}

core/src/main/resourceExtensions/pack.mcmeta

@@ -12,6 +12,10 @@
       {
         "formats": { "min_inclusive": 22 },
         "directory": "mc1_20_3"
+      },
+      {
+        "formats": { "min_inclusive": 67 },
+        "directory": "mc_1_21_9"
       }
     ]
   }