Add missing Holder and Delegate fields to binary-codec definitions

The Holder field (AccountID nth=11) and Delegate field (AccountID nth=12) were missing
from the definitions.json, causing MPTokenAuthorize transactions with the Holder field
to fail with tecNO_PERMISSION because the field was not being properly serialized.

This fix aligns the definitions with the official xrpl.js ripple-binary-codec.

Author: bleprevost

binary-codec/definitions/definitions.json

@@ -2197,6 +2197,26 @@
         "type": "AccountID"
       }
     ],
+    [
+      "Holder",
+      {
+        "nth": 11,
+        "isVLEncoded": true,
+        "isSerialized": true,
+        "isSigningField": true,
+        "type": "AccountID"
+      }
+    ],
+    [
+      "Delegate",
+      {
+        "nth": 12,
+        "isVLEncoded": true,
+        "isSerialized": true,
+        "isSigningField": true,
+        "type": "AccountID"
+      }
+    ],
     [
       "HookAccount",
       {