Add heaviest subtree utility functions (#10863)

Co-authored-by: Carl <carl@solana.com>

runtime/src/bank_utils.rs

@@ -0,0 +1,28 @@
+use crate::{
+    bank::Bank,
+    genesis_utils::{self, GenesisConfigInfo, ValidatorVoteKeypairs},
+};
+use solana_sdk::{
+    pubkey::Pubkey,
+    signature::{Keypair, Signer},
+};
+
+pub fn setup_bank_and_vote_pubkeys(num_vote_accounts: usize, stake: u64) -> (Bank, Vec<Pubkey>) {
+    // Create some voters at genesis
+    let validator_voting_keypairs: Vec<_> = (0..num_vote_accounts)
+        .map(|_| ValidatorVoteKeypairs::new(Keypair::new(), Keypair::new(), Keypair::new()))
+        .collect();
+
+    let vote_pubkeys: Vec<_> = validator_voting_keypairs
+        .iter()
+        .map(|k| k.vote_keypair.pubkey())
+        .collect();
+    let GenesisConfigInfo { genesis_config, .. } =
+        genesis_utils::create_genesis_config_with_vote_accounts(
+            10_000,
+            &validator_voting_keypairs,
+            stake,
+        );
+    let bank = Bank::new(&genesis_config);
+    (bank, vote_pubkeys)
+}