EIP-695: Create `eth_chainId` method for JSON-RPC

[pedrouid]

I think this thread is relevant for the discussion of the EIP-1637

EIP-1637 - Adding chainId parameter to eth_sendTransaction

Following the discussion from the Wallet ring regarding a new scope of JSON-RPC methods prefixed with wallet_ to improve Wallet UX, I propose that existing signing methods such as eth_sendTransaction, eth_sendRawTransaction and eth_signTransaction would benefit a lot from a small change that would be backwards-compatible and easily changed by major JS libraries used as middleware between Dapps and Wallets