Add ConfirmedBlock struct, and rework Blocktree apis to include block…

[CriesofCarrots]

…hash info and dummy tx statuses

Problem

The getConfirmedBlock rpc endpoint only returns part of the data needed about a confirmed block by our main downstream use case. It is missing blockhash, previous_blockhash, and real transaction status data.

Summary of Changes

• Adds RpcConfirmedBlock struct, to organize data needed from Blocktree and to be returned by RPC
• Extends Blocktree api to get blockhash and previous_blockhash for a confirmed block
• Adds Blocktree api to map transactions to their statuses. This does not yet return real transaction status data, but moves the generation of dummy statuses from rpc.rs up into blocktree.rs, ready to be plugged in after feat: rocksdb (persistent) transaction status cache #6958 and implementation of writes into that store

Toward #6867

This will break getConfirmedBlock in https://github.com/solana-labs/solana-web3.js again
(sorry, @jstarry ...)

[codecov]

Codecov Report

Merging #7004 into master will decrease coverage by 2.3%.
The diff coverage is 63.4%.

@@           Coverage Diff            @@
##           master   #7004     +/-   ##
========================================
- Coverage    78.8%   76.4%   -2.4%     
========================================
  Files         223     223             
  Lines       42948   44307   +1359     
========================================
+ Hits        33856   33890     +34     
- Misses       9092   10417   +1325

Pull request has been modified.