Co-authored-by: Josh Soref <jsoref@users.noreply.github.com>
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## Summary of the Pull Request
Upgrade check-spelling to [v0.0.18](https://github.com/check-spelling/check-spelling/releases/tag/v0.0.18)
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## References
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## PR Checklist
* [ ] Closes #xxx
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [ ] Schema updated.
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
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## Detailed Description of the Pull Request / Additional comments
I've replaced the `dictionary` directory with `allow` and `reject`. When terminal got check-spelling, I didn't have a way to do `allow`/`reject` (but they were added a while ago). With this release, the bot will complain about items that are in user managed files that wouldn't be valid, this is mostly `-`s in dictionary files, but it also includes numbers `0`..`9` and `_`. If a specific token needs to be accepted but not its sub-elements, the item should be added to `patterns.txt` instead (`D2DERR_SHADER_COMPILE_FAILED` is an example).
With this version, check-spelling defaults to only considering tokens with at least 3 letters. It's possible to tune it back to 2 (or even 1), but in testing, the 2 character tokens have ended up not being worthwhile. (This can be [adjusted](https://github.com/check-spelling/check-spelling/wiki/Configuration#shortest_word) if it turns out that people manage to misspell two character tokens often enough to justify checking them.)
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## Validation Steps Performed
I ran a number of passes of the spell checker in https://github.com/check-spelling/terminal/actions (note: I tend to delete this repository, so this link may be dead at some point, and action run logs expire).
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