Move Context into Noir interfaces initialiser

[spalladino]

Today, the autogenerated Noir interfaces take a private or public context on every call as their first parameter. We can take a page out of the refactor that @benesjan did for storage in #1926, and do the same for interfaces.

So instead of doing:

let token = Token::at(address);
token.transfer(&mut context, to, amount);

We'd be doing:

let token = Token::at(address, Context::private(&mut context));
token.transfer(to, amount);

Note that we should wait until #2074 is implemented before moving forward though. Also, note that Context::private(&mut context) can probably be autogenerated by a macro.

[iAmMichaelConnor]

Great suggestion!

[iAmMichaelConnor]

let token = Token::at(address, Context::private(&mut context));

Can we instead do:
let token = Token::at(address, &mut context);?

[spalladino]

Definitely. I forgot I had split the interfaces into public and private, and each of them takes a public context or private context respectively, so there's no need to use the Context union from #2074.