Added a `uint256 evmChainId` state variable to the Core, Token and NFT Bridge
contracts. `evmChainId` is compared to `block.chainid` in the `chainId`
function. When they don't match, a "bad fork" Chain ID is returned,
otherwise the Wormhole Chain ID is returned.
This allows requesting attestations for various commitment/confirmation levels. This is helpful for low-latency applications like Pyth.
Change-Id: Ib49ace163365106b227613d2f66b787b3e5f5461