Refactor: process_instruction() (#20448)

* Adds first_instruction_account parameter to process_instruction().

* Removes InvokeContext::remove_first_keyed_account() from all BPF loaders.

* Removes InvokeContext::remove_first_keyed_account() from all builtin programs.

* Removes InvokeContext::remove_first_keyed_account() from all mock ups.

* Deprecates InvokeContext::remove_first_keyed_account().

* Documents index base of keyed_account_at_index().

* Adds dynamic offset to call sites of "keyed_account_at_index()".

runtime/benches/bank.rs

@@ -33,6 +33,7 @@ const NOOP_PROGRAM_ID: [u8; 32] = [
 #[allow(clippy::unnecessary_wraps)]
 fn process_instruction(
     _program_id: &Pubkey,
+    _first_instruction_account: usize,
     _data: &[u8],
     _invoke_context: &mut dyn InvokeContext,
 ) -> Result<(), InstructionError> {