Whisk: Move validator whisk trackers and commitments to state

[dapplion]

Current whisk implementation #3342 requires to add two extra data structures per validator: one whisk tracker (container or two G1 points) and one k commitment (G1 point).

Instead of extending the validator container two include those two items, this PR adds two new lists in the state. This approach has the advantages:

• Reduces the additional hashing load from +4 hashes / val record to +2 hashes / val record
• Prevents adding 1 extra depth to the validator type tree
• Simplifies implementation, as clients are used to beacon state fields changing every fork, but the Validator type has remained constant since phase0 and is heavily used. At least in Lighthouse and Lodestar, changing the Validator class has a significant higher implementation cost than changing the beacon state.

[asn-d6]

This is pretty much done. Left some comments for discussion. Perhaps none of them need any actual actions.

[asn-d6]

Thanks! LGTM!