Capella: Validator index in Withdrawal?

[mcdee]

Looking at the Withdrawal type, is there value to having the validator index in here? At current there doesn't seem to be a way of tying a withdrawal to a particular validator (even if the beacon state root were available in the EVM) so this would provide that linkage.

[djrtwo]

I'm not opposed. It comes at a cost to block size but other than that seems safe/fine.

The current idea is that the withdrawal_index can be tracked when created for the validator but that's not very offline-proof

[hwwhww]

close via #3050