fix(sdk-coin-apt): add getter for sender pubkey

Ticket: COIN-2891

Author: at31416

modules/sdk-coin-apt/src/lib/transaction/transaction.ts

@@ -177,6 +177,10 @@ export abstract class Transaction extends BaseTransaction {
     this._senderSignature = { publicKey, signature };
   }
 
+  getFeePayerPubKey(): string {
+    return this._feePayerSignature.publicKey.pub;
+  }
+
   addFeePayerSignature(publicKey: PublicKey, signature: Buffer): void {
     this._feePayerSignature = { publicKey, signature };
   }

modules/sdk-coin-apt/src/lib/transactionBuilder.ts

@@ -159,4 +159,8 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
   addFeePayerAddress(address: string): void {
     this.transaction.addFeePayerAddress(address);
   }
+
+  getFeePayerPubKey(): string {
+    return this.transaction.getFeePayerPubKey();
+  }
 }