Check composite field count during validation

This is a temporary (and inefficient) workaround to check number
of fields in Cadence CompositeValue.

In the future, CompositeValue.FieldCount() will be added to
Cadence, so that function can be used to improve this workaround.

cmd/util/ledger/migrations/cadence_value_validation.go

@@ -273,6 +273,7 @@ func cadenceCompositeValueEqual(
 	}
 
 	var err *validationError
+	vFieldNames := make([]string, 0, 10) // v's field names
 	v.ForEachField(nopMemoryGauge, func(fieldName string, fieldValue interpreter.Value) bool {
 		otherFieldValue := otherComposite.GetField(otherInterpreter, interpreter.EmptyLocationRange, fieldName)
 
@@ -282,9 +283,26 @@ func cadenceCompositeValueEqual(
 			return false
 		}
 
+		vFieldNames = append(vFieldNames, fieldName)
 		return true
 	})
 
+	// TODO: Use CompositeValue.FieldCount() from Cadence after it is merged and available.
+	otherFieldNames := make([]string, 0, len(vFieldNames)) // otherComposite's field names
+	otherComposite.ForEachField(nopMemoryGauge, func(fieldName string, _ interpreter.Value) bool {
+		otherFieldNames = append(otherFieldNames, fieldName)
+		return true
+	})
+
+	if len(vFieldNames) != len(otherFieldNames) {
+		return newValidationErrorf(
+			"composite %s fields differ: %v != %v",
+			v.TypeID(),
+			vFieldNames,
+			otherFieldNames,
+		)
+	}
+
 	return err
 }