Add support for the new composer installed.json format (#32310) (#32331)

Co-authored-by: Jakub Arbet <jakub.arbet@protonmail.com>

src/Illuminate/Foundation/PackageManifest.php

@@ -111,7 +111,9 @@ public function build()
         $packages = [];
 
         if ($this->files->exists($path = $this->vendorPath.'/composer/installed.json')) {
-            $packages = json_decode($this->files->get($path), true);
+            $installed = json_decode($this->files->get($path), true);
+
+            $packages = $installed['packages'] ?? $installed;
         }
 
         $ignoreAll = in_array('*', $ignore = $this->packagesToIgnore());