Add list check

[janine-c]

What does this PR do?

New rule that checks for ordered lists that start with letters rather than numbers, because those lists render funny.

Motivation

Example of funny rendering:

Example of detection with new rule:

Release

• YES, this PR requires a release
• NO, this PR doesn't need a release

Additional Notes

There are a bunch of parakeets running wild around London, and no one knows where they came from.

Release checklist

• Create zip files for EACH style folder.
• Attach the zip files when creating a release.

[maycmlee]

Thanks for adding this! I'm not actually sure how I should review this, so let me know if there is something specific I should be checking 😄

[janine-c]

Thanks for taking a look, @maycmlee! If you want, you can switch to this branch (and probably quit and restart VS Code), and then see if you're seeing the detections that I put in my screenshot. I think as long as it's flagging lettered lists, it's working as intended!