Try: Add CSS Custom Properties to CSS types

[DaniGuardiola]

Context: #60560 (comment)

Through this augmentation, CSS Custom Properties are supported (type-wise) in the style prop of React elements. They need to start with --. This is only applied to the components package, and could be extended to other packages by just copying the ambient declaration file.

[github-actions]

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[github-actions]

Flaky tests detected in ef75828.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/9194100898
📝 Reported issues:

• [Flaky Test] Clicking on inserter while on zoom-out should open the patterns tab on the inserter #61806 in /test/e2e/specs/site-editor/zoom-out.spec.js

[mirka]

Good one 👍 I'm fine with keeping it components-only for now, since there doesn't seem to be any relevant usage outside of the package.

[tyxla]

Thank you @DaniGuardiola, this has been bugging me for ages 🙌