Use parent blockhash to seed EpochRewardsHasher

[CriesofCarrots]

Problem

Partitioned rewards code requires exposing the parent bank's hash to clients trying to find stake rewards, because that is the seed used for the partition hasher:

solana/runtime/src/bank.rs

Line 2360 in 166be29

&self.parent_hash(),

The EpochRewardsHasher calls this the parent_block_hash

solana/runtime/src/epoch_rewards_hasher.rs

Line 45 in 166be29

parent_block_hash: &Hash,

, so it's unclear which hash was intended.

Either way, it will certainly be easier for clients if we use the blockhash, since this is already stored in block metadata (and can be easily looked up).

Summary of Changes

Update Bank::calculate_rewards_for_partitioning() to pass the parent blockhash to EpochRewardsHasher::calculate_rewards_for_partitioning()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (166be29) 81.7% compared to head (39e87e2) 81.8%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34744   +/-   ##
=======================================
  Coverage    81.7%    81.8%           
=======================================
  Files         823      823           
  Lines      222865   222865           
=======================================
+ Hits       182262   182319   +57     
+ Misses      40603    40546   -57     

[t-nelson]

lgtm!

cc/ @HaoranYi for viz

[HaoranYi]

yes. lgtm!