This also rolls back the `TerminalWorkDir` abstraction I added for the
original remoting, and tidies up the terminal creation code to be clear
about whether we're creating a task *or* a terminal. The previous logic
was a little muddy because it assumed we could be doing both at the same
time (which was not true).
Release Notes:
- remoting alpha: Removed the ability to specify `gh cs ssh` or `gcloud
compute ssh` etc. See https://zed.dev/docs/remote-development for
alternatives.
- remoting alpha: Added support for terminal and tasks to new
experimental ssh remoting
583b6235fb