Changeset 60750

Build: Update Gutenberg integration to checkout-and-build approach.

This changes WordPress Core's Gutenberg integration from npm packages to checking out and building Gutenberg directly. Instead of syncing individual npm packages, Core now checks out the Gutenberg repository, builds it, and copies the build artifacts.

This enables Core to use Gutenberg's advanced features like route-based navigation, full-page rendering, and the Font Library, while also streamlining future updates.

New commands:

• npm run gutenberg:checkout - Clones Gutenberg at a specified ref
• npm run gutenberg:build - Runs Gutenberg's build process
• npm run gutenberg:copy - Copies and transforms build output to Core
• npm run gutenberg:integrate - Runs all three steps

Main changes:

• Removes webpack configs replaced by Gutenberg's build (blocks.js, packages.js, script-modules.js, development.js, vendors.js)
• Adds Font Library page (/wp-admin/font-library.php)
• Adds copy scripts to transform Gutenberg plugin paths to Core paths
• Moves vendor copy step from webpack to Gruntfile

New year, new process. Happy New Year!

Props youknowriad, ellatrix, sirreal, westonruter, desrosj, tellthemachines.
Fixes #64393.

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