Add validator_index to Withdrawal.

specs/capella/beacon-chain.md

@@ -111,6 +111,7 @@ We define the following Python custom types for type hinting and readability:
 ```python
 class Withdrawal(Container):
     index: WithdrawalIndex
+    validator_index: ValidatorIndex
     address: ExecutionAddress
     amount: Gwei
 ```
@@ -275,6 +276,7 @@ def withdraw_balance(state: BeaconState, validator_index: ValidatorIndex, amount
     # Create a corresponding withdrawal receipt
     withdrawal = Withdrawal(
         index=state.next_withdrawal_index,
+        validator_index=validator_index,
         address=ExecutionAddress(state.validators[validator_index].withdrawal_credentials[12:]),
         amount=amount,
     )

tests/core/pyspec/eth2spec/test/capella/block_processing/test_process_withdrawals.py

@@ -13,6 +13,7 @@ def prepare_withdrawal_queue(spec, state, num_withdrawals):
     for i in range(num_withdrawals):
         withdrawal = spec.Withdrawal(
             index=i + 5,
+            validator_index=i + 1000,
             address=b'\x42' * 20,
             amount=200000 + i,
         )
@@ -110,6 +111,7 @@ def test_fail_empty_queue_non_empty_withdrawals(spec, state):
     execution_payload = build_empty_execution_payload(spec, state)
     withdrawal = spec.Withdrawal(
         index=0,
+        validator_index=0,
         address=b'\x30' * 20,
         amount=420,
     )