Google Fonts: Fix font detection when fallback families are present

[mreishus]

Proposed changes

The google fonts module can leave out a font when its value includes fallbacks. For example:

• var(--wp--preset--font-family--inter) - Found correctly
• var(--wp--preset--font-family--inter), sans-serif - Left out because it doesn't end in ).

Fix the regex and add tests. I had Astra do this.

Related product discussion/links

Partially fixes #50180

Does this pull request change what data or activity we track or use?

No

Testing instructions

1. Enable the Google Fonts module.
2. Use a theme that registers a bundled font in theme.json.
3. Set styles.typography.fontFamily to reference that font with a fallback, such as var(--wp--preset--font-family--inter), system-ui, sans-serif.
4. Load the front end. Check that the page includes an @font-face rule for the selected font.
5. Remove the fallback families. Check that the font-face rule still appears.
6. Run the google-font-face PHP test suite.

[github-actions]

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/modules/google-fonts/current/class-jetpack-google-font-face.php	70/83 (84.34%)	84.34%	-70 💚

Full summary · PHP report · JS report

[mreishus]

Tested on JN site + Beta. Confirmed that @font-face is appearing on 2023 theme with styles:

"typography": {
    "fontFamily": "var(--wp--preset--font-family--inter), system-ui, sans-serif",
    "fontSize": "var(--wp--preset--font-size--medium)",
    "lineHeight": "1.6"
}

set in theme.json