[New command] `exercism cd`

### Problem

We find newcomers raising issues unable to run test and submit commands. Recent example: https://github.com/exercism/exercism/issues/5313 but I have seen many before. They usually don't `cd` into the exercise directory before running commands and are confused by all the errors.

### Feature Request

We have `exercism workspace` command which prints workspace path. It would be nice to have a command to `cd` into exercise directory given a track and exercise slug.

```bash
exercism cd track slug
```

We can then modify our READMEs asking users to run this command before running commands like `test` and `submit`. It will also take care of cross-platform paths with forward and backward slashes which installation/exercise instructions don't have to worry about.

### Alternatives

We can use workspace command with bash eval, but I am not sure if this will work with windows.

```bash
cd `exercism workspace`/javascript/hello-world
```