Consider builder pending payments for pending balance to withdraw

The helper function to keep track of pending balances to withdraw should
take into account any pending payments and pending withdrawals from
builders.

[] - Add regression test for a payload with a withdrawal request from
the current builder, that would invalidate a builder pending payment
otherwise.

Author: potuz

specs/gloas/beacon-chain.md

@@ -37,6 +37,7 @@
     - [New `is_valid_indexed_payload_attestation`](#new-is_valid_indexed_payload_attestation)
     - [New `is_parent_block_full`](#new-is_parent_block_full)
   - [Misc](#misc-2)
+    - [Modified `get_pending_balance_to_withdraw`](#modified-get_pending_balance_to_withdraw)
     - [New `remove_flag`](#new-remove_flag)
     - [New `compute_balance_weighted_selection`](#new-compute_balance_weighted_selection)
     - [New `compute_balance_weighted_acceptance`](#new-compute_balance_weighted_acceptance)
@@ -436,6 +437,32 @@ def is_parent_block_full(state: BeaconState) -> bool:
 
 ### Misc
 
+#### Modified `get_pending_balance_to_withdraw`
+
+*Note*: `get_pending_balance_to_withdraw` is modified to account for pending
+builder payments.
+
+```python
+def get_pending_balance_to_withdraw(state: BeaconState, validator_index: ValidatorIndex) -> Gwei:
+    return (
+        sum(
+            withdrawal.amount
+            for withdrawal in state.pending_partial_withdrawals
+            if withdrawal.validator_index == validator_index
+        )
+        + sum(
+            withdrawal.amount
+            for withdrawal in state.builder_pending_withdrawals
+            if withdrawal.builder_index == validator_index
+        )
+        + sum(
+            payment.withdrawal.amount
+            for payment in state.builder_pending_payment
+            if payment.withdrawal.builder_index == validator_index
+        )
+    )
+```
+
 #### New `remove_flag`
 
 ```python