Icons: Add label search support to WP_Icons_Registry

[t-hamano]

Trac ticket: https://core.trac.wordpress.org/ticket/64847

Backport WordPress/gutenberg#75878

Use of AI Tools

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Caution

Commit this PR after the wp/7.0 release branch has been created. This PR targets the 7.1 release.

[github-actions]

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