Restore: Sync Gutenberg @ 2ee7ede6be6d4e55d5c7047394c5c4e0ea8d521d

See changelog in b00a9eb

> Build/Test Tools: Only include active, stable routes in build.
> The `registry.php` file within the built assets from the `gutenberg` repository contains an accurate list of active, stable routes. However, the `build/routes/` directory has the JavaScript and PHP files for all routes, regardless of their status.
>
> This makes adjustments to the `grunt copy` tasks responsible for copying these files into the appropriate locations to extract the list of routes specified in the `registry.php` file so that only the required files are copied.

Author: desrosj