EVM: DST20 v2 burn of sent amount

[Jouzo]

Summary

• Remove original contract storage update from precompile
• Use internal DST20 _burn method instead
• Fix total supplies issues
• Add tests for burn event
• Fixes EVM: token transfers on stock split (upgradeToken) misses inflow #2909

Implications

• Consensus
  • changi rollback

[Bushstar]

If we are no longer going to zero the old token amount then we should not deduct that amount from the economy Gov vars as it still exists inside EVM on the burn address.

[Jouzo]

We do zero it through calling the internal _burn method which handles deducting the total supply. You can see on the first screenshot that the META/v1 total supply is now correctly zeroed out

[Jouzo]

function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _totalSupply -= amount;
        }

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }

Our implementation consider the burn as a reduction of totalSupply.
It's our appreciation how sending to the burn address should be counted for the gov vars economy. I would say that deducting it sounds right since it won't be accessible.

require(from != address(0), "ERC20: transfer from the zero address"); checks are scatted in the other methods and prevent the burn address from sending any amount

[Bushstar]

That sounds good to me. We can leave the economy Gov vars as they are.