This makes sure that the behaviour of the CLI matches that of the UI.
In Zed itself we always open a new window (e.g. when clicking on Open
Project in new window in the recent projects picker), but in the CLI we
where re-using existing windows even when specifying
"cli_default_open_behavior": "new_window".
This caused confusion, so this PR ensures that we always open a new
window, even if that folder is already open. We still focus the active
window in the case where the path is a subpath of a project that is
already open.

Can be tested with

```
cd crates/cli
cargo run -- --zed ../../target/debug/zed somefolder
```

Release Notes:

- cli: Ensure `zed somefolder` always opens a new window, even when
`cli_default_open_behavior` is set to `new_window` and the project is
already open