Media: Re-introduce client-side media processing feature

[adamsilverstein]

Summary

• Reverts the removal in [62081] now that WordPress 7.1 has forked
• Restores all PHP functions, REST API endpoints, cross-origin isolation infrastructure, VIPS script module handling, build configuration, and associated tests
• 14 files restored, ~1,625 lines

Test plan

• CI passes (coding standards, PHPUnit, JS tests)
• Verify client-side media processing functions are restored in wp-includes/media.php
• Verify REST API endpoints for attachments are restored
• Verify cross-origin isolation test suite passes
• Verify VIPS script module registration is restored

Trac ticket: https://core.trac.wordpress.org/ticket/64919

Props adamsilverstein, jorbin.
See #64906.

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Props adamsilverstein.

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[github-actions]

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