Add missing Istanbul gas costs

[holgerd77]

Added missing Istanbul gas costs for:

• ChainID opcode (EIP-1344, as base param …in chainstart)
• Blake2b precompile (EIP-2129/152)
• Calldata gas cost reduction (EIP-2028)

Wasn't sure about this referenced G_BASE parameter for the ChainID opcode addition mentioned in the EIP. Py-EVM is just integrating it as a generic constant. I did a parameter search in Common and the VM and couldn't find a reference to that (maybe I missed), so I decided to add this here in a generic way to chainstart.

Maybe @rmeissner - who worked out the EIP and also did some work on the VM - could help with a comment on that.

[rmeissner]

I took the G_BASE from the yellow paper.
Quote: G base - 2 - Amount of gas to pay for operations of the set W base.

Edit: maybe this is reflected here: https://github.com/ethereumjs/ethereumjs-common/pull/58/files#diff-17e7800cbf4bde014712cf3b079a4f45R25

[s1na]

The base gas cost for opcodes are defined in the VM. Example for an opcode that has G_BASE is ADDRESS. Snippets from ethereumjs-vm and py-evm

  0x30: ['ADDRESS', 2, true],

    opcode_values.ADDRESS: as_opcode(
        logic_fn=context.address,
        mnemonic=mnemonics.ADDRESS,
        gas_cost=constants.GAS_BASE,
    ),

[s1na]

The other two changes look good. I can approve if you'd rather keep G_BASE here, rather than hardcoded in the VM.

[holgerd77]

@s1na I would tend to leave it here, we might want to also update on the VM side or - if for the moment too distracting - at least add some TODO note on this.

But feel free to point out some objection if you don't like this for some reason.

[s1na]

Looks good