EVM: Convert CALLACTOR into a precompile

[Stebalien]

It's really annoying to call arbitrary assembly from solidity. We should define a new precompile that takes:

1. An actor address.
2. A method number.
3. A codec number.
4. Parameter bytes.

It'll re-use the value and gas limit from the precompile call itself.

This precompile returns a struct with the following fields:

1. The exit code (non-negative) or error number (negative).
2. The return codec or 0 if there isn't a return value.
3. The return value bytes.