Calculate refunds on VM side

[chfast]

It should be VM's responsibility to calculate and aggregate refunds.

• Add "refund" filed to evmc_result.

[axic]

daytona depends on this.

[jlokier]

Nowadays refunds depend on information only known by the Host when the EVM calls setStorage, and I think that's quite a neat separation of concerns and knowledge. So perhaps this issue should be closed.

[chfast]

We are providing a lot of information about the SSTORE status to allow proper gas counting inside VM: https://github.com/ethereum/evmc/blob/master/include/evmc/evmc.h#L510-L536. There may be cases not handled by this where gas cost is the same but the refund is different, but I don't think we need very different mechanism to handle it fully.