* Implement CreditOnlyLocks
* Update credit-only atomic on account load
* Update credit-only atomic after bank.freeze_lock; store credits if all credit-only lock references are dropped
* Commit credit-only credits on bank freeze
* Update core to CreditAccountLocks
* Impl credit-only in System Transfer
* Rework CreditAccountLocks, test, and fix bugs
* Review comments: Pass CreditAccountLocks by reference; Tighten up insert block
* Only store credits on completed slot
* Check balance in bench_exchange funding to ensure commit_credits has completed
* Add is_debitable info to KeyedAccount meta to pass into programs
* Reinstate CreditOnlyLocks check on lock_account
* Rework CreditAccountLocks to remove strong_count usage
* Add multi-threaded credit-only locks test
* Improve RwLocks usage
* Review comments: panic if bad things happen; tighter code
* Assert lock_accounts race does not happen
* Revert panic if bad things happen; not a bad thing
* Add credit-only debit/data check to verify_instruction
* Store credits and pass to accounts_db
* Add InstructionErrors and tests
* Relax account locks for credit-only accounts
* Collect credit-only account credits before passing to accounts_db to store properly
* Convert System Transfer accounts to credit-only, and fixup test
* Functionalize collect_accounts to unit test
* Review comments
* Rebase
* Refactor Storage Program
* Replace KeyedAccount trait with StorageAccount struct
* Implement State for Account, not StorageAccount
* Make State trait more generic
* Move validation check into function
* Rename userdata to data
Instead of saying "userdata", which is ambiguous and imprecise,
say "instruction data" or "account data".
Also, add `ProgramError::InvalidInstructionData`
Fixes#2761
