This includes a new TargetAddrs field on both Run and RunCreateOptions
which we'll use to send resource addresses that were specified using
-target on the CLI command line when using the remote backend.

There were some unrelated upstream breaking changes compared to the last
version we had vendored, so this commit also includes some changes to the
backend/remote package to work with this new API, which now requires the
remote backend to be aware of the remote system's opaque workspace id.