Global Styles: Migrate shadows presets to use the preset management layer.

[juanfra]

What?

Built on top of #79810

Migrate the shadow presets to use the layer proposed in #79810. No functionality should be changing There may be a few minimal spacing changes due to the introduction of the recommended Stack component from @wordpres/ui. All strings stay unchanged.

Why?

Adopts the new shared preset-management layer (#79810) to remove duplicated code between preset managers, and to make it cheaper to add the next preset screens (Spacing, Border Radius) on top of it.

How?

Migrating to use <PresetGroup>, usePresets(), <PresetEditHeader> and the dialogs for renaming/deleting.

Testing Instructions

1. Go to Site Editor > Styles > Shadows
2. Custom: add a shadow, add/remove/edit parts (color, inset, x/y/blur/spread), rename, delete, then "Remove all custom shadows".
3. Theme/Default (if your theme provides shadow.presets.theme or has shadow.defaultPresets on): edit a preset's value, confirm Reset is enabled in the edit menu, restore it, confirm Reset disables again.
4. Delete a shadow while its edit screen is open. Confirm it navigates back cleanly.

Storybook

• Run npm run storybook:dev
• Go to Global Styles UI and check how the shadows are behaving with the new preset management.

Use of AI Tools

Cursor/Claude

[github-actions]

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Co-authored-by: juanfra <juanfra@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[github-actions]

Size Change: +191 B (0%)

Total Size: 7.82 MB

📦 View Changed

Filename	Size	Change
build/scripts/edit-site/index.min.js	311 kB	+8 B (0%)
build/scripts/editor/index.min.js	510 kB	+183 B (+0.04%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 8c60253.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/30153193269
📝 Reported issues:

• [Flaky Test] Filtering #76250 in /test/e2e/specs/site-editor/new-templates-list.spec.js

[juanfra]

Since rebasing we were getting an ESLint failure coming from #80754, which added some components to the not-recommended denylist. For now I'm suppressing them (same as #80754 did) and I'll treat them separately so this PR doesn't grow in scope or risk.

[Mamaduka]

Works as expected. Thanks, @juanfra!

[juanfra]

Thanks a lot for the reviews George!