[Suggestion]: Some unusable module functions for normal users have existed

[0xOutOfGas]

Desc:
Some block and transaction-related module functions must be called under account GENESIS_ADDRES. Since these functions are not allowed for normal users to access, remove or hide them away from normal users. Removing or hiding these functions can reduce risk and many code lines.

Code Location:
sources/TransactionManager.move, sources/Block.move, sources/BlockReward.move, sources/Account.move

Functions:

// below functions can't be called from normal users

TransactionManager::block_prologue, TransactionManager::epilogue
Block::process_block_metadata
BlockReward::process_block_reward
Account::txn_prologue, Account::txn_epilogue

[jolestar]

This is a historical problem, as the friend function was not supported by Move in the early days.

If we want to change it to friend now, we have to deprecate the old function and use a new function name and let the new one to friend function.

@sanlee42