Media: Make client-side supported MIME types configurable

[adamsilverstein]

Summary

Add a client_side_supported_mime_types filter and REST API index field so plugins can customize which image formats are processed client-side via WebAssembly-based vips.

• Adds client_side_supported_mime_types filter with default list: image/jpeg, image/png, image/gif, image/webp, image/avif
• Exposes the filtered value in the REST API root index response (for users with upload_files capability)
• Updates preload paths in both post editor and site editor to include the new field

Changes

• src/wp-includes/rest-api/class-wp-rest-server.php — Add filter and REST index field
• src/wp-admin/edit-form-blocks.php — Add field to preload paths
• src/wp-admin/site-editor.php — Add field to preload paths
• tests/qunit/fixtures/wp-api-generated.js — Update test fixture

Related

• Gutenberg PR: Media: Make client-side supported MIME types configurable gutenberg#76549

Trac ticket: https://core.trac.wordpress.org/ticket/64876

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