If --function-signature is used with --version 2, then also include the return type/attributes in the check lines. This is the implementation of D133943 rebased on the --version mechanism from D142473.
This doesn't bump the default version yet, because I'd like to do that together with D140212 (which enables --function-signature by default), as these changes seem closely related. For now this functionality can be accessed by explicitly passing --version 2 to UTC.