Update theme json and style engine to support border radius presets for WP 6.9

[andrewserong]

This PR builds on what was proposed in #9406, but adds tests and fixes up an issue where the former PR didn't yet update the valid settings array.

Trac ticket: https://core.trac.wordpress.org/ticket/63799#ticket

This PR brings the changes from the following Gutenberg PR to core: WordPress/gutenberg#67544 for support for border radius presets.

Changes include:

• definitions of presets settings for theme.json
• CSS var settings for style engine

Testing instructions:

Check that the PHP tests pass, but you can also run these tests locally if you so desire:

npm run test:php -- --filter Tests_wpStyleEngine
npm run test:php -- --filter Tests_Theme_wpThemeJson

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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 aaronrobertshaw, andrewserong, ramonopoly, mukesh27.

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[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

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Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
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Test this pull request with WordPress Playground.

[ramonjd]

I double-checked against WordPress/gutenberg#67544 (which was already tested in context)

LGTM

[andrewserong]

Thanks folks! I'll commit this tomorrow 👍

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 60892
GitHub commit: dc9dc24

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.