Icons: Support keyword-based search in the icons registry

[n8finch]

Backports WordPress/gutenberg#82367.

Registered icons can now carry an optional keywords property, and icon search matches against it in addition to the icon's name and label. Previously an icon could only be found by its namespaced name or its human-readable label, so an icon whose common name differs from its label (for example core/menu, widely known as a "hamburger" menu) was undiscoverable in the editor's icon picker unless the user happened to guess the label.

This follows the same pattern as the label search added in [62551] for #64847.

Changes

WP_Icons_Registry

• register() accepts an optional keywords property. It must be an array of strings; anything else triggers _doing_it_wrong() and the icon is not registered. Accepted keywords are passed through sanitize_text_field().
• New protected icon_matches_search() encapsulates the match, testing the search term case-insensitively against the icon's name, label, and keywords.
• get_registered_icons() delegates to it, replacing the inlined name/label comparison.

REST API (WP_REST_Icons_Controller)

• keywords is added to the item schema as a read-only array of strings.
• The field is always present in a response, defaulting to an empty array for icons registered without keywords, so clients that filter locally do not have to special-case its absence.

Core icon manifest

• _wp_register_default_icons() passes a manifest entry's keywords through to wp_register_icon().
• src/wp-includes/assets/icon-library-manifest.php is regenerated from the Gutenberg branch, adding localized keywords to all 88 core icons. Keywords use the icon keyword translation context, matching the existing icon label context.

Testing instructions

Automated:

npm run test:php -- --test-suffix wpIconsRegistry.php,wpRestIconsController.php tests/phpunit/tests/icons

Eight new test methods cover registration with and without keywords, rejection of non-string and non-array values (seven data-provided cases), case-insensitive keyword matching, keyword search through the REST endpoint, and the empty-array default. The full icons group passes: 131 tests, 518 assertions.

Manual testing requires the update to Gutenberg plugin: WordPress/gutenberg#82367

Trac ticket: https://core.trac.wordpress.org/ticket/66158

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: Diagnosing failures in the initial backport commits, regenerating the icon manifest from the Gutenberg branch, correcting the REST controller's keywords handling, removing a test that covered a plugin-only code path with no Core equivalent, and aligning docblocks with the Inline Documentation Standards. I reviewed every change, ran the test suite, and take responsibility for the result.

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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.

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[github-actions]

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[t-hamano]

LGTM! I believe the Gutenberg implementation has been correctly backported to core. In 3596cc0, I added the ticket number to the test, which is standard practice when adding unit tests to core.

[t-hamano]

I re-tested this PR and confirmed that all the feedback from the Gutenberg PR (WordPress/gutenberg#76481) has been properly backported here 👍

[github-actions]

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

SVN changeset: 63999
GitHub commit: 3ffb1df

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