theme_importer: Add `--output` flag for outputting the theme to a file (#7486)

```bash
cargo run -p theme_importer -- dark-plus-syntax-color-theme.json --output output.json
```

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
45cf36e870d1y committed on 2/7/2024, 9:23:36 PM· committed by GitHubparente6dad23
2 files changedLine totals unavailable