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.

runtime/src/lib.rs

@@ -29,6 +29,7 @@ pub mod status_cache;
 mod system_instruction_processor;
 pub mod transaction_batch;
 pub mod transaction_utils;
+pub mod vote_account;
 pub mod vote_sender_types;
 
 extern crate solana_config_program;