build: FoP Proxy Manager for Symfony bridge compatibility (#1494)

Author: piotrkreft

composer.json

@@ -71,6 +71,7 @@
         "behatch/contexts": "^3.3",
         "escapestudios/symfony2-coding-standard": "^3.10",
         "friends-of-behat/symfony-extension": "^2.0.5",
+        "friendsofphp/proxy-manager-lts": "^1.0",
         "infection/infection": "^0.17.5",
         "malukenho/docheader": "^0.1.8",
         "nelmio/alice": "^3.6",