* 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()".
