Assembler: Use variation partials and move styles.blocks.variations to styles.variations

[richtabor]

Follow up to https://github.com/WordPress/gutenberg/pull/62712, which adjusts where block style variations are defined with in theme style variations, as well as better leveraging style variation partials.

To test, load up https://github.com/WordPress/gutenberg/pull/62712, then change to alternate color palettes. It should work exactly as previously.

[richtabor]

Relies on https://github.com/WordPress/gutenberg/pull/62712 merged, into Gutenberg and perhaps for WordPress 6.6.

[github-actions[bot]]

Preview changes

I've detected changes to the following themes in this PR: Alves, Vitrum, Cookbook, Assembler, Varia.

You can preview these changes by following the links below:

• Preview changes for Alves (child of varia)
• Preview changes for Vitrum
• Preview changes for Cookbook
• Preview changes for Assembler
• Preview changes for Varia

I will update this comment with the latest preview links as you push more changes to this PR. ⚠️ Note: The preview sites are created using WordPress Playground. You can add content, edit settings, and test the themes as you would on a real site, but please note that changes are not saved between sessions.

⚠️ Note: Child themes are dependent on their parent themes. You will have to install the parent theme as well for the preview to work correctly.

[glendaviesnz]

Tested well for me on Gutenberg trunk (18.7RC) and WP 6.5.5

[richtabor]

Went ahead and tweaked the form input styles to work better across all block style variations as well.