Implement vm.computeCreatedAddress cheatcode

[anvacaru]

Adds support for Foundry's vm.computeCreateAddress(address, uint256) cheatcode, which predicts the address a
The contract will be deployed via CREATE using a deployer address and nonce.

Changes:

• cheatcodes.md: new rule cheatcode.call.computeCreateAddress that decodes (deployer, nonce) from calldata and
  computes the CREATE address by applying RLP encoding and keccak256
• ComputeCreateAddress.t.sol: end-to-end test verifying the predicted address matches the actual deployed
  contract address.

[palinatolmach]

I left a small recommendation on the documentation and agree with @ehildenb's suggestion to add a test similar to the real-world example (I guess it would be using the output of computeCreateAddress to instantiate a proxy), otherwise lgtm!