Extractor: preserves the first comment in the file [Closes #100]

Author: dg

src/PhpGenerator/Extractor.php

@@ -208,6 +208,10 @@ public function enterNode(Node $node)
 			}
 		};
 
+		if ($this->statements) {
+			$this->addCommentAndAttributes($phpFile, $this->statements[0]);
+		}
+
 		$traverser = new PhpParser\NodeTraverser;
 		$traverser->addVisitor($visitor);
 		$traverser->traverse($this->statements);
@@ -367,6 +371,7 @@ private function addCommentAndAttributes($element, Node $node): void
 			$comment = $node->getDocComment()->getReformattedText();
 			$comment = Helpers::unformatDocComment($comment);
 			$element->setComment($comment);
+			$node->setDocComment(new PhpParser\Comment\Doc(''));
 		}
 
 		foreach ($node->attrGroups ?? [] as $group) {

tests/PhpGenerator/expected/Extractor.classes.expect

@@ -1,5 +1,9 @@
 <?php
 
+/**
+ * First comment
+ */
+
 declare(strict_types=1);
 
 namespace Abc;

tests/PhpGenerator/fixtures/classes.php

@@ -1,7 +1,15 @@
 <?php
 
+/**
+ * First comment
+ */
+
 declare(strict_types=1);
 
+/**
+ * Second comment
+ */
+
 namespace Abc;
 
 /**