Administration: Add a reusable .delete-link CSS class

[devsupportlogicrays]

Trac ticket: https://core.trac.wordpress.org/ticket/36882

Summary

• Adds a reusable .delete-link admin CSS class for destructive action links.
• Mirrors the existing .button-link-delete color rules (base + hover/focus) in the admin color schemes.
• Gives plugin and theme authors a standard class instead of reusing unrelated core selectors or copying red link styles by hand.

Test plan

• Confirm .wp-core-ui .delete-link uses the alert-red color in an admin screen
• Confirm hover/focus lightens/darkens consistently with .button-link-delete
• Confirm existing .button-link-delete buttons are unchanged
• Spot-check at least one admin color scheme (e.g. Default / Modern)

[github-actions]

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