Block Editor: Include navigation block server logic.

Core did not include the navigation block PHP files.
This commit fixes the issue referred, and now the navigation block is executed on the frontend. The block still does not work as expected and throws an error during frontend execution. That problem is going to be fixed on the next WordPress package update.
This commit adds the file as it is on the npm package used.

Props gziolo.
Fixes #49348.
Built from https://develop.svn.wordpress.org/trunk@47176


git-svn-id: https://core.svn.wordpress.org/trunk@46976 1a063a9b-81f0-0310-95a4-ce76da25c4cd