feat(fonts): merge families

[florian-lefebvre]

Changes

• Feedback from Discord
• Before, it was not possible to only download font files for weights normal 500, italic 500 and normal 600. This is because a font family is defined by a combination of weights and styles, so you'd necessarily have to also download italic 600
• Now, families that have the same cssVariable, name and provider will be merged
• This PR also adds a warning log if there are several unmergeable families (same cssVariable but different name/provider)

Testing

Manually tested, unit tests added

Docs

• Changesets
• RFC update: withastro/roadmap@d73b578 (#1039)
• Docs: feat(fonts): merge families docs#12696

[changeset-bot]

🦋 Changeset detected

Latest commit: de30f3c

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

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[codspeed]

CodSpeed Performance Report

Merging #14750 will not alter performance

_{Comparing feat/fonts-merge-families (de30f3c) with main (18c55e1)¹}

Summary

✅ 6 untouched

Footnotes

1. No successful run was found on main (72381ef) during the generation of this report, so 18c55e1 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[ematipico]

Left just a nit