Pass Reference of External Call Context

[samliok]

Forces ExternalCallContext to be passed by reference. This allows programs to reuse the same context without having to create a new one for each external call.

[iFrostizz]

I'm just wondering if it would make sense to also borrow the fields inside of the ExternalCallContext, for instance you cannot do:

#[public]
pub fn inc(_: Context, external: Program, address: Address) {
    let ctx = ExternalCallContext::new(external, 1_000_000, 0);
    counter::inc(&ctx, address, 1);
    let ctx = ExternalCallContext::new(external, 1_000_000, 0);
    counter::inc(&ctx, address, 1);
}

because external is moved since Program doesn't implement Copy nor we (probably) want