Guidelines: Update actions-section and import/export workflow

[aswasif007]

What?

Related issue: #76384

Refactors the Content Guidelines “Actions” section (import/export/revert) and improves the guidelines import/export flows.

Why?

• Improve maintainability by extracting a dedicated action row component and consolidating rendering/styling.
• Use ConfirmDialog component instead of using a custom modal to seek confirmation for import.
• Make exports easier to track by including the export date in the downloaded filename.

How?

• Render actions from a single ACTIONS definition and use a new GuidelineAction component for each row.
• On import, clear categories/blocks not present in the JSON (so omissions remove existing guidelines instead of leaving stale values).
• Export downloads as guidelines-YYYY-MM-DD.json.

Testing Instructions

1. Open the Content Guidelines page/route.
2. Scroll to Actions.
3. Click Download and confirm the filename is guidelines-YYYY-MM-DD.json.
4. Click Upload, select a valid guidelines JSON file, and confirm a dialog appears warning that current guidelines will be replaced.
5. Click Continue and verify:
   • A success snackbar appears.
   • Guidelines update to match the imported content.
   • Categories/blocks omitted from the imported file are removed/cleared.
6. Try importing an invalid JSON (or wrong schema) and verify an error Notice appears and is dismissible.
7. Click View history and verify it navigates to revision history.

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Co-authored-by: aswasif007 <aswasif007@git.wordpress.org>

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