[Feature Request] Make use of new API for including last heartbeat details when failing activity tasks

[Sushisource]

Is your feature request related to a problem? Please describe.

Server now supports this. Using it can simplify internal logic. Of course we still have to support the old path for backwards compat... So maybe not worth doing this until it's been released long enough that we don't have to.

Describe the solution you'd like

Additional context

[cretz]

One wonders if we can add a server capability that you can check. Otherwise, one does wonder how old of a server version we are expected to support.