* Refactor Bank::load_and_execute_transactions
* Refactor: improve type safety of TransactionExecutionResult
* Add enum for extra type safety in execution results
* feedback
* Makes error handling in BorrowedAccount optional.
Adds BorrowedAccount ::get_rent_epoch().
Exposes InstructionContext::get_index_in_transaction().
Turns accounts and account_keys into pinned boxed slices.
* Introduces "unsafe" to InvokeContext::push().
* Turns &TransactionContext into &mut TransactionContext in InvokeContext.
* Push and pop InstructionContext in InvokeContext.
Makes test_process_cross_program and test_native_invoke symmetric.
Removes the borrow check from test_invoke_context_verify.
* Removes keyed_accounts from prepare_instruction()
* Removes usage of invoke_stack.
* Removes keyed_accounts from program-test.
* Removes caller_write_privileges.
* Removes keyed_accounts from BPF parameter (de-)serialization.
* Turns compute_units_consumed of ProcessInstructionResult into a &mut parameter.
* Removes second nesting level from test_process_instruction_compute_budget().
* Makes test_process_cross_program and test_native_invoke symmetric.
* Unifies test_process_cross_program(), test_native_invoke() and test_process_instruction_compute_budget() into test_process_instruction().
* Add more-legitimate conversion from legacy Transaction to SanitizedTransaction
* Add Banks method with preflight checks
* Expose BanksClient method with preflight checks
* Unwrap simulation err
* Add Bank simulation method that works on unfrozen Banks
* Add simpler api
* Better name: BanksTransactionResultWithSimulation
* Adds TransactionContext, InstructionContext and BorrowedAccount.
* Redirects the usage of accounts in InvokeContext through TransactionContext.
Also use the types declared in transaction_context.rs everywhere.
* Adjusts all affected tests.
* Unifies all InstructionRecorders of a transaction into one.
* Stops explicitly compiling CPI instructions for recording,
uses the indices gathered from instruction_accounts instead.
* Introduces InstructionAccount which is like AccountMeta but uses an index instead of a Pubkey
* Renames InvokeContext::create_message() to InvokeContext::prepare_instruction()
* Removes Message and CompiledInstruction from InvokeContext interfaces.
* Resolves TODOs of sol_invoke_signed() in program-test.
* Moves CompiledInstruction::visit_each_account() into invoke_context.rs
* Removes Rc from Rc<RefCell<AccountSharedData>> in the program-runtime.
* Adjusts tests in bpf_loader, system_instruction_processor, config_processor, vote_instruction and stake_instruction
