Reorder font stack to prefer Segoe

[ellynliu]

Task: task-487561

Link: preview-622

On Windows computers, use Segoe UI. Segoe UI is not available on Mac and Linux, so fallback to Segoe UI Variable Text. After that, fallback to the remaining fonts in the font stack.

Testing

1. Review changes.
2. Checkout ellyn/fonts and npm start. On Windows, you should see that the font is still Segoe UI.

Contributor checklist

• Did you update the description of this pull request with a review link and test steps?
• Did you submit a changeset? Changesets are required for all code changes.
• Does your pull request implement complex UI logic (js/ts)? Consider adding an integration test to test your user flow.
• Does your pull request add a new page to the documentation site? Add your new page for automated accessibility testing in /integration/tests/accessibility.

[changeset-bot]

🦋 Changeset detected

Latest commit: 18fca7f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@microsoft/atlas-css	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR