Gloas modify get_pending_balance_to_withdraw

[shane-moore]

Changes per spec

• modified get_pending_balance_to_withdraw

How this works

There are a couple places in the codebase where we want to verify that a validator has no pending balances to withdraw before allowing them to initiate an exit or consolidation. Pre-gloas, we were calling get_pending_balance_to_withdraw to check whether their BeaconState.pending_partial_withdrawals was empty and if so, let them proceed. Since gloas introduces BeaconState.builder_pending_payments and BeaconState.builder_pending_withdrawals, we now have to account for these pending validator balances as well before letting them proceed with an exit or consolidation.

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