Navigation overlay: backport patterns and template part definition

[MaggieCabrera]

This PR backports core PHP changes from Gutenberg that remove the overlay experiment and migrate navigation overlay patterns to use the core namespace.

This backport includes the following core changes:

1. Navigation Pattern Category: Adds the navigation block pattern category registration in block-patterns.php.

2. Navigation Overlay Patterns: Adds five new navigation overlay block patterns.

3. Template Part Area Constant: Adds the WP_TEMPLATE_PART_AREA_NAVIGATION_OVERLAY constant and corresponding area definition in block-template-utils.php to support navigation overlay template parts.

This backport is based on changes from WordPress/gutenberg#74968

Testing

• Verify navigation pattern category appears in the block pattern inserter
• Verify all five navigation overlay patterns are available and render correctly
• Verify navigation overlay template parts can be created and used
• Test pattern insertion in the site editor

Trac ticket: https://core.trac.wordpress.org/ticket/64589

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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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[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props onemaggie, scruffian, get_dave, mikachan.

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[mikachan]

This is testing well for me 🙌

• Verify navigation pattern category appears in the block pattern inserter ✅
• Verify all five navigation overlay patterns are available and render correctly ✅
• Verify navigation overlay template parts can be created and used ✅
• Test pattern insertion in the site editor ✅
• Pattern naming and descriptions make sense ✅

If there are any issues, we can address them during the beta period.

[getdave]

Rebase and then we should be good to land 🙏

[github-actions]

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

SVN changeset: 61609
GitHub commit: db26faa

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