* Adds methods based on instruction_account_index to InstructionContext.
Removes methods which are based on index_in_instruction.
* Adjusts program-runtime.
* Adjusts runtime.
* Adjusts bpf loader.
* Adjusts built-in programs.
* Adjusts program-test and bpf tests.
* Replaces all use sites of get_sysvar_with_account_check by get_sysvar_with_account_check2.
* Removes get_sysvar_with_account_check.
* Renames get_sysvar_with_account_check2 to get_sysvar_with_account_check.
* Adds get_sysvar_with_account_check2 for ABIv2.
* Replaces get_signers() and get_sysvar_with_account_check() in system_instruction_processor.
* Replaces KeyedAccount by BorrowedAccount in nonce_keyed_account.
* Replaces from_keyed_account() by SysvarCache in stake instruction.
* Replaces from_keyed_account() by SysvarCache in system instruction processor.
* Removes from_keyed_account().
Moves check_sysvar_keyed_account() into sysvar_cache.rs
* Removes tests which test for incorrectly serialized sysvars.
* Unifies SysvarCache filling in the runtime and tests.
Removes new_mock_with_sysvars_and_features()
Removes mock_process_instruction_with_sysvars().
Replaces from_keyed_account() by SysvarCache in vote processor.
* Replaces from_keyed_account() by SysvarCache in BPF loader.