DNA: update all references to Jetpack_Error to use Error package instead

Follow-up from #12701.

Let's update all uses of `Jetpack_Error` to use the Error package instead.
Let's take that opportunity to deprecate `Jetpack_Error` just in case others outside of Jetpack rely on that class today.

Start by reviewing follow-up issue #12701, then search the repository for all uses of `Jetpack_Error` and its definition. The work is done when references use the Error package and `Jetpack_Error` is deprecated for external users that may still rely on it.

Written by the indexing model from the issue text.