[Symfony] Prepended ezplatform configuration to ezpublish extension

This is a workaround to avoid copying all the code from
EzPublishCoreBundle at once. It allows using "ezplatform"
as a root node for the configuration w/o defining that configuration.

Validation is still done by ezpublish extension.

src/EzPlatformCoreBundle/bundle/DependencyInjection/Configuration.php

@@ -20,9 +20,12 @@ class Configuration implements ConfigurationInterface
      */
     public function getConfigTreeBuilder(): TreeBuilder
     {
-        $treeBuilder = new TreeBuilder(EzPlatformCoreExtension::EXTENSION_ALIAS);
+        $treeBuilder = new TreeBuilder();
 
-        $rootNode = $treeBuilder->getRootNode();
+        $rootNode = $treeBuilder->root(EzPlatformCoreExtension::EXTENSION_ALIAS);
+
+        // @todo define actual configuration (move from EzPublishCoreBundle)
+        $rootNode->variablePrototype();
 
         return $treeBuilder;
     }

src/EzPlatformCoreBundle/bundle/DependencyInjection/EzPlatformCoreExtension.php

@@ -11,24 +11,40 @@
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Extension\Extension;
+use Symfony\Component\DependencyInjection\Extension\PrependExtensionInterface;
 
-final class EzPlatformCoreExtension extends Extension
+final class EzPlatformCoreExtension extends Extension implements PrependExtensionInterface
 {
     public const EXTENSION_ALIAS = 'ezplatform';
 
     public function load(array $configs, ContainerBuilder $container): void
     {
-        $configuration = $this->getConfiguration($configs, $container);
-        $config = $this->processConfiguration($configuration, $configs);
     }
 
-    public function getConfiguration(array $config, ContainerBuilder $container): ConfigurationInterface
-    {
+    public function getConfiguration(
+        array $config,
+        ContainerBuilder $container
+    ): ConfigurationInterface {
         return new Configuration();
     }
 
     public function getAlias(): string
     {
         return self::EXTENSION_ALIAS;
     }
+
+    /**
+     * Prepend "ezplatform" configuration to "ezpublish" configuration.
+     *
+     * @todo remove once we replace EzPublishCoreBundle with EzPlatformCoreBundle
+     */
+    public function prepend(ContainerBuilder $container): void
+    {
+        // inject "ezplatform" extension settings into "ezpublish" extension
+        // configuration here is zero-based array of configurations from multiple sources
+        // to be merged by "ezpublish" extension
+        foreach ($container->getExtensionConfig('ezplatform') as $eZPlatformConfig) {
+            $container->prependExtensionConfig('ezpublish', $eZPlatformConfig);
+        }
+    }
 }