Instead of keeping a validator key list per EpochRef, this PR introduces
a single shared validator key list in ChainDAG, and cleans up some other
ChainDAG and key-related issues.
The PR does not introduce the validator key list in the state transition
- this is because we batch-check all signatures before entering the spec
code, thus the spec code never hits the cache.
A future refactor should _probably_ remove the threadvar altogether.
There's a few other small fixes in here that make the flow easier to
read:
* fix `var ChainDAGRef` -> `ChainDAGRef`
* fix `var QuarantineRef` -> `QuarantineRef`
* consistent `dag` variable name
* avoid using threadvar pubkey cache in most cases
* better error messages in batch signature checking
* use StateData in place of BeaconState outside state transition code
* propagate more StateData usage
* remove withStateVars().state
* wrap get_beacon_committee(BeaconState, ...) as gbc(StateData, ...)
* switch makeAttestation() to use StateData
* use StateData wrapper/dispatcher for get_committee_count_per_slot()
* convert AttestationCache.init(), weak subjectivity functions, and updateValidatorMetrics()
* add get_shuffled_active_validator_indices(StateData) and get_block_root_at_slot(StateData)
* switch makeAttestationData() to StateData
* sync AllTests-mainnet.md after rebase