Blocks: Add of prop to Subtitle

[joaonunomota]

Closes part of #22490

What I did

• Add support for of prop via useOf with "meta" as only valid type
• Default to extracting content from parameters.docs.subtitle
• Deprecate extracting content from parameters.componentSubtitle
• Add stories for several possible applications of Subtitle
• Update docs and migration files
• Fix typo in EmptyExample

How to test

1. Run yarn storybook:blocks
2. Open Storybook in your browser
3. Access Subtitle stories

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[kylegach]

Thanks for updating the API reference! ❤️

Could you please keep these props in alphabetical order?

[joaonunomota]

Sorted :)

[joaonunomota]

@JReinhold Hi! Is there anything that I can update / fix for a pull request review? It would be nice if this PR and #23728 could go out with #23849.

[JReinhold]

Sorry @joaonunomota I've missed this. I'll review this early next week

[ndelangen]

@JReinhold please review?

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[JReinhold]

Thank you for the fantastic work, I'm sorry it took so long for me to properly review it. <3