caches vote-state de-serialized from vote accounts (#13795)

Gossip and other places repeatedly de-serialize vote-state stored in
vote accounts. Ideally the first de-serialization should cache the
result.

This commit adds new VoteAccount type which lazily de-serializes
VoteState from Account data and caches the result internally.

Serialize and Deserialize traits are manually implemented to match
existing code. So, despite changes to frozen_abi, this commit should be
backward compatible.

frozen-abi/src/abi_example.rs

@@ -188,6 +188,7 @@ example_impls! { f32, 0.0f32 }
 example_impls! { f64, 0.0f64 }
 example_impls! { String, String::new() }
 example_impls! { std::time::Duration, std::time::Duration::from_secs(0) }
+example_impls! { std::sync::Once, std::sync::Once::new() }
 
 use std::sync::atomic::*;