* Moves stack_height of the instruction_trace into InstructionContext.
* Uses nesting_level instead of stack_height internally in transaction_context.rs
* Uses the instruction_trace instead of the instruction_context_stack internally.
* Adds feature gate: record_instruction_in_transaction_context_push.
* 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.
Alexander Meißner
Michael Vines
Jack May
Greg Fitzgerald