feat: add native Xdebug support (dunglas#271)

* feat: add native Xdebug support

* cleanup

* fix review

* fix review

* Improve docs

* some more improvements

* remove useless env var

Author: dunglas

docker/php/conf.d/symfony.ini

@@ -0,0 +1,13 @@
+expose_php = 0
+date.timezone = UTC
+apc.enable_cli = 1
+session.use_strict_mode = 1
+zend.detect_unicode = 0
+
+; https://symfony.com/doc/current/performance.html
+realpath_cache_size = 4096K
+realpath_cache_ttl = 600
+opcache.interned_strings_buffer = 16
+opcache.max_accelerated_files = 20000
+opcache.memory_consumption = 256
+opcache.enable_file_override = 1