fix(OnyxIcon): revert default size back to 24px

[larsrickert]

Relates to #1307

We changed the default icon size to match the parent font size in #1307 which caused a lot of unintended changes in Storybook examples and our docs. Also to match the parent font size is a rare use case so we change back the default size back to 24px to better fit common use cases.

Checklist

• [x] The added / edited code has been documented with JSDoc
• [x] A changeset is added with npx changeset add if your changes should be released as npm package (because they affect the library usage)

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 83e160df67ff54c73a0911db59ec104e9e42dd4c

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

This PR includes changesets to release 7 packages

| Name | Type | | ------------------------- | ----- | | sit-onyx | Major | | alpha-test-app | Patch | | playground | Patch | | @sit-onyx/chartjs-plugin | Major | | @sit-onyx/nuxt | Major | | @sit-onyx/storybook-utils | Major | | @sit-onyx/vitepress-theme | Major |

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