Add support for the EvmAddress type

[nfurfaro]

Sway has an EvmAddress type which is very similar to the Address type.
It would be nice to be able to use the type as contract call inputs and outputs.

*Note: An EVM address is only 20 bytes, so the first 12 bytes of the inner value are set to zero

/// The Address type, a struct wrappper around the inner `value`.
pub struct EvmAddress {
    value: b256,
}