Altair consensus changes and refactors (#2279)

## Proposed Changes

Implement the consensus changes necessary for the upcoming Altair hard fork.

## Additional Info

This is quite a heavy refactor, with pivotal types like the `BeaconState` and `BeaconBlock` changing from structs to enums. This ripples through the whole codebase with field accesses changing to methods, e.g. `state.slot` => `state.slot()`.


Co-authored-by: realbigsean <seananderson33@gmail.com>

consensus/tree_hash/examples/flamegraph_beacon_state.rs

@@ -1,26 +1,46 @@
-use types::test_utils::TestingBeaconStateBuilder;
+use beacon_chain::store::StoreConfig;
+use beacon_chain::test_utils::{BeaconChainHarness, EphemeralHarnessType};
 use types::{BeaconState, EthSpec, MainnetEthSpec};
 
 const TREE_HASH_LOOPS: usize = 1_000;
 const VALIDATOR_COUNT: usize = 1_000;
 
-fn build_state<T: EthSpec>(validator_count: usize) -> BeaconState<T> {
-    let (state, _keypairs) =
-        TestingBeaconStateBuilder::from_deterministic_keypairs(validator_count, &T::default_spec())
-            .build();
+fn get_harness<T: EthSpec>() -> BeaconChainHarness<EphemeralHarnessType<T>> {
+    let harness = BeaconChainHarness::new_with_store_config(
+        T::default(),
+        None,
+        types::test_utils::generate_deterministic_keypairs(VALIDATOR_COUNT),
+        StoreConfig::default(),
+    );
 
-    assert_eq!(state.validators.len(), validator_count);
-    assert_eq!(state.balances.len(), validator_count);
-    assert!(state.previous_epoch_attestations.is_empty());
-    assert!(state.current_epoch_attestations.is_empty());
-    assert!(state.eth1_data_votes.is_empty());
-    assert!(state.historical_roots.is_empty());
+    harness.advance_slot();
+
+    harness
+}
+
+fn build_state<T: EthSpec>() -> BeaconState<T> {
+    let state = get_harness::<T>().chain.head_beacon_state().unwrap();
+
+    assert_eq!(state.as_base().unwrap().validators.len(), VALIDATOR_COUNT);
+    assert_eq!(state.as_base().unwrap().balances.len(), VALIDATOR_COUNT);
+    assert!(state
+        .as_base()
+        .unwrap()
+        .previous_epoch_attestations
+        .is_empty());
+    assert!(state
+        .as_base()
+        .unwrap()
+        .current_epoch_attestations
+        .is_empty());
+    assert!(state.as_base().unwrap().eth1_data_votes.is_empty());
+    assert!(state.as_base().unwrap().historical_roots.is_empty());
 
     state
 }
 
 fn main() {
-    let state = build_state::<MainnetEthSpec>(VALIDATOR_COUNT);
+    let state = build_state::<MainnetEthSpec>();
 
     // This vec is an attempt to ensure the compiler doesn't optimize-out the hashing.
     let mut vec = Vec::with_capacity(TREE_HASH_LOOPS);