message: [lang] Add check for &self or &mut self args in message signatures
diff: @@ -97,6 +97,21 @@ impl Contract {
  )
  }
  };
  + for msg in messages.iter() {
  + let inputs = &msg.sig.decl.inputs;
  + {
  + let self_ty: &ast::FnArg = inputs.first().unwrap().into_value();
  + match self_ty {
  + ast::FnArg::SelfValue(_) | ast::FnArg::Captured(_) => {
  + bail!(
  + self_ty,
  + "contract messages must start with `&self` or `&mut self`"
  + )
  + }
  + _ => ()
  + }
  + }
  + }
  Ok((deploy_handler, messages, methods))
  }
  