`try-runtime::fast-forward` (#12896)

* try-runtime::fast-forward

* Revert un`pub`ing command's fields

* Handle storage change failure

* Adjust Substrate node

* Feature-gated imports

* doc link

* Feature-gated imports in node-template

* Move trait, blanket implementation and auxiliary functions to a new module

* Distinguish between plain babe+timestamp and substrate enhanced info

* Remove uncles inherents

* Missing argument

* Add doc comment about `blocktime_millis`

* Add licenses