Global Styles: Add missing block style variation defaults

[aaronrobertshaw]

Backports the default block style variation styles to the core theme.json file after the general specificity reduction of global styles in WordPress/gutenberg#61638.

To test:

1. Prior to checking out this branch, visit the site editor and edit the home page with TT4 active
2. Select the button and switch its block style to Outline. Note the appearance doesn't change.
3. Checkout this branch and repeat the steps. The Outline style should take effect.

Trac ticket: https://core.trac.wordpress.org/ticket/61165

Before	After

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Props aaronrobertshaw.

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[github-actions]

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Test this pull request with WordPress Playground.

[tellthemachines]

Thanks for following up with this! Testing shows this PR fixes the issue of Button Outline variation styles not being added to the rule that ensures they have priority over element styles.

Before:

After:

[tellthemachines]

Committed in r58393.