bug symfony#14266 [HttpKernel] Check if "symfony/proxy-manager-bridge" package is installed (hason)

This PR was merged into the 2.3 branch.

Discussion
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[HttpKernel] Check if "symfony/proxy-manager-bridge" package is installed

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

Commits
-------

43cc877 [HttpKernel] Check if "symfony/proxy-manager-bridge" package is installed

Author: fabpot

src/Symfony/Component/HttpKernel/Kernel.php

@@ -662,7 +662,7 @@ protected function getContainerBuilder()
     {
         $container = new ContainerBuilder(new ParameterBag($this->getKernelParameters()));
 
-        if (class_exists('ProxyManager\Configuration')) {
+        if (class_exists('ProxyManager\Configuration') && class_exists('Symfony\Bridge\ProxyManager\LazyProxy\Instantiator\RuntimeInstantiator')) {
             $container->setProxyInstantiator(new RuntimeInstantiator());
         }
 
@@ -682,7 +682,7 @@ protected function dumpContainer(ConfigCache $cache, ContainerBuilder $container
         // cache the container
         $dumper = new PhpDumper($container);
 
-        if (class_exists('ProxyManager\Configuration')) {
+        if (class_exists('ProxyManager\Configuration') && class_exists('Symfony\Bridge\ProxyManager\LazyProxy\PhpDumper\ProxyDumper')) {
             $dumper->setProxyDumper(new ProxyDumper(md5((string) $cache)));
         }