feat(abstract-utxo): add isUtxoWalletData function

Issue: BTC-1801

Author: OttoAllmendinger

modules/abstract-utxo/src/wallet.ts

@@ -1,14 +1,21 @@
 import { Wallet, WalletData } from '@bitgo/sdk-core';
 
+import { isUtxoCoinName, UtxoCoinName } from './names';
+
 // parseTransactions' return type makes use of WalletData's type but with customChangeKeySignatures as required.
 export interface UtxoWalletData extends WalletData {
+  coin: UtxoCoinName;
   customChangeKeySignatures: {
     user: string;
     backup: string;
     bitgo: string;
   };
 }
 
+export function isUtxoWalletData(obj: WalletData): obj is UtxoWalletData {
+  return isUtxoCoinName(obj.coin);
+}
+
 export interface UtxoWallet extends Wallet {
   _wallet: UtxoWalletData;
 }