Move preprocessing logic into Preprocessor class

[MAILPOET-2286]

Additional preprocessing logic is needed to handle WooCommerce
blocks, so instead of making the Renderer class even bigger,
I am creating a new Preprocessor class. I wanted to move the
`addMailpoetLogoContentBlock` logic as well but it will break
tests and require a lot of refactor to fix them so I am leaving
it here for now.

lib/Newsletter/Renderer/Preprocessor.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace MailPoet\Newsletter\Renderer;
+
+use MailPoet\Newsletter\Renderer\Blocks\Renderer as BlocksRenderer;
+
+class Preprocessor {
+
+  /** @var BlocksRenderer */
+  private $blocks_renderer;
+
+  public function __construct(BlocksRenderer $blocks_renderer) {
+    $this->blocks_renderer = $blocks_renderer;
+  }
+
+  /**
+   * @param array $content
+   * @return array
+   */
+  public function process($content) {
+    if (!array_key_exists('blocks', $content)) {
+      return $content;
+    }
+    $blocks = [];
+    foreach ($content['blocks'] as $block) {
+      if ($block['type'] === 'automatedLatestContentLayout') {
+        $blocks = array_merge(
+          $blocks,
+          $this->blocks_renderer->automatedLatestContentTransformedPosts($block)
+        );
+      } else {
+        $blocks[] = $block;
+      }
+    }
+    $content['blocks'] = $blocks;
+    return $content;
+  }
+}

lib/Newsletter/Renderer/Renderer.php

@@ -13,6 +13,7 @@ use MailPoet\WP\Functions as WPFunctions;
 class Renderer {
   public $blocks_renderer;
   public $columns_renderer;
+  private $preprocessor;
   public $CSS_inliner;
   public $newsletter;
   public $preview;
@@ -30,7 +31,8 @@ class Renderer {
     $this->preview = $preview;
     $this->blocks_renderer = new Blocks\Renderer($this->newsletter);
     $this->columns_renderer = new Columns\Renderer();
-    $this->CSS_inliner = new \MailPoetVendor\CSS();
+    $this->preprocessor = new Preprocessor($this->blocks_renderer);
+    $this->CSS_inliner = new \MailPoet\Util\CSS();
     $this->template = file_get_contents(dirname(__FILE__) . '/' . self::NEWSLETTER_TEMPLATE);
     $this->premium_activated = License::getLicense();
     $bridge = new Bridge();
@@ -53,7 +55,7 @@ class Renderer {
       $content = $this->addMailpoetLogoContentBlock($content, $styles);
     }
 
-    $content = $this->preProcessALC($content);
+    $content = $this->preprocessor->process($content);
     $rendered_body = $this->renderBody($content);
     $rendered_styles = $this->renderStyles($styles);
     $custom_fonts_links = StylesHelper::getCustomFontsLinks($styles);
@@ -78,30 +80,6 @@ class Renderer {
       $rendered_newsletter;
   }
 
-  /**
-   * @param array $content
-   * @return array
-   */
-  private function preProcessALC(array $content) {
-    $blocks = [];
-    $content_blocks = (array_key_exists('blocks', $content))
-      ? $content['blocks']
-      : [];
-    foreach ($content_blocks as $block) {
-      if ($block['type'] === 'automatedLatestContentLayout') {
-        $blocks = array_merge(
-          $blocks,
-          $this->blocks_renderer->automatedLatestContentTransformedPosts($block)
-        );
-      } else {
-        $blocks[] = $block;
-      }
-    }
-
-    $content['blocks'] = $blocks;
-    return $content;
-  }
-
   /**
    * @param array $content
    * @return string