[engine] Fix withdrawal fee estimates

[LayneHaber]

Describe the bug
Withdrawals use a hardcoded fee because they cannot estimate without sigs. This does not account for the WithdrawHelper calls. We should be estimating the WithdrawHelper fees and adding those into the amount we account for in the gas calculations.

During implementation should also consider the edge case where the quote is requested without a callData field, and callData is supplied to the engine API. (Quote should not be valid in this case)