Refactor: Remove KeyedAccount from program runtime (#22226)

* 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.

program-runtime/src/native_loader.rs

@@ -170,7 +170,7 @@ impl NativeLoader {
         invoke_context: &mut InvokeContext,
     ) -> Result<(), InstructionError> {
         let (program_id, name_vec) = {
-            let program_id = invoke_context.get_caller()?;
+            let program_id = invoke_context.transaction_context.get_program_key()?;
             let keyed_accounts = invoke_context.get_keyed_accounts()?;
             let program = keyed_account_at_index(keyed_accounts, first_instruction_account)?;
             if native_loader::id() != *program_id {