🧑‍💻(tokens) add getThemesFromGlobals utils

Export a new util method `getThemesFromGlobals` to easily generate theme with
its variant only by providing a partial globals object. By default it returns
both available theme variants (light & dark). Through options you can prefix
variant property keys, only generate theme with a subset of variant and also
overrides/extend theme.

.changeset/seven-lands-wash.md

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+"@gouvfr-lasuite/cunningham-tokens": minor
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+Add getThemesFromGlobals util