* Add accounts_index bench
* Don't take the accounts index lock unless needed
* Accounts_index remove insert return vec and add capacity stats
* Use hashbrown hashmap for accounts_index
* Be able to create bank snapshots
* fix clippy
* load snapshot on start
* regenerate account index from the storage
* Remove rc feature dependency
* cleanup
* save snapshot for slot 0
* Add optional depth parameter to pubsub, and store in subscriptions
* Pass bank_forks into rpc_subscription; add method to check depth before notify and impl for account subscriptions
* Impl check-depth for signature subscriptions
* Impl check-depth for program subscriptions
* Plumb fork id through accounts
* Use fork id and root to prevent repeated account notifications; also s/Depth/Confirmations
* Write tests in terms of bank_forks
* Fixup accounts tests
* Add pubsub-confirmations tests
* Update pubsub documentation
* Revert "Revert "account storage is not in sync with the index after gc (#3914)" (#3936)"
This reverts commit 4f47fc00bc.
* fix get_exclusive_storage
* clippy
* account storage is not in sync with the index after gc
* builds
* clippy fmt
* test
* purge dead forks on store
* rm println
* also fixed count_stores
* comments