minor #9678 [HttpKernel] use static late binding when dumping out container (tgabi333)

This PR was submitted for the 2.2 branch but it was merged into the 2.3 branch instead (closes #9678).

Discussion
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[HttpKernel] use static late binding when dumping out container

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no?
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |  #9649
| License       | MIT
| Doc PR        |

This PR gives the ability to override the stripComments method in descendants (and to disable the memory-eater container whitespace stripping)

Commits
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2e241cc [HttpKernel] use static late binding when dumping out container

Author: fabpot

Kernel.php

@@ -714,7 +714,7 @@ protected function dumpContainer(ConfigCache $cache, ContainerBuilder $container
 
         $content = $dumper->dump(array('class' => $class, 'base_class' => $baseClass));
         if (!$this->debug) {
-            $content = self::stripComments($content);
+            $content = static::stripComments($content);
         }
 
         $cache->write($content, $container->getResources());