Add aspect ratio presets support via theme.json

[fabiankaegy]

Trac ticket: https://core.trac.wordpress.org/ticket/61239

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Core Committers: Use this line as a base for the props when committing in SVN:

Props fabiankaegy, isabel_brison.

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[github-actions]

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Test this pull request with WordPress Playground.

[tellthemachines]

Aside from the annotation, changes LGTM and work as expected when following the testing steps in WordPress/gutenberg#47271!

[tellthemachines]

Committed in r58242.