[Blueprints v2] Constraint the Blueprint bundle format

The Blueprints v2 spec defines a required bundle directory structure. Let's make sure any bundle not following this structure is rejected by the PHP runner. cc @janjakes

blueprint.json
wp-content/
└─── plugins/
|    └─── akismet.zip
|    └─── custom-meta-box.php
|    └─── hello-dolly/
|         └─── hello-dolly.php
└─── mu-plugins/
|    └─── 0-check-integrity.zip
└─── themes/
|    └─── twentytwentythree/
|         └─── style.css
|         └─── functions.php
|         └─── screenshot.jpg
└─── languages/
|    └─── plugins/
|         └─── akismet/
|              └─── akismet-en_US.po
|              └─── akismet-en_US.mo
|              └─── akismet-de_DE.po
|              └─── akismet-de_DE.mo
|    └─── themes/
|         └─── twentytwentythree/
|              └─── twentytwentythree-en_US.po
|              └─── twentytwentythree-en_US.mo
|    └─── en_US.po
|    └─── en_US.mo
|    └─── de_DE.po
|    └─── de_DE.mo
└─── uploads/
|    └─── fonts/
|         └─── open-sans.woff2
|         └─── roboto.woff2
|         └─── ...
|    └─── 2024/
|         └─── 01/
|              └─── image.jpg
|              └─── video.mp4
|              └─── audio.mp3
|              └─── document.pdf
|              └─── other.txt
└─── content/
     └─── dump-1.sql
     └─── dump-2.sql
     └─── dump-3.sql
     └─── bike-repair-shop.wxr
     └─── posts/
           └─── posts/
				└─── 2025-01-01-my-first-post.html
           └─── pages/
                └─── books/
                     └─── post-type.json
                     └─── the-old-man-and-the-sea.html
                     └─── harry-potter.md