Feature request: support {:termination false} on classes as well as traits

[robin-aws]

This trait is currently only supported on traits, but it would be very easy to also look for it on classes extending traits in other modules. The advantage would be being able to leave the attribute off of traits in shared libraries, such that users of such libraries would receive the error about termination checking being unsound in the presence of dynamic dispatch (#1588), and have to explicitly opt in to this in their code, as opposed to library authors opting in on their reusable traits and hiding this problem from users.