[PHP-Symfony] Encurage Symfony 5 bundle directory structure best practices (#13014)

* use .yaml instead of .yml

This is recommended by Symfony standards

* save Bundle files also to src path

* add test for generate ping

* add package imports

* fix expected file names

* why is Api/ApiServer.php missing

* output filenames

* use getAbsolutePath for debug purpose

* do not use punctuation as current directory

* refactor: remove todos

* use also .yaml in test to fix it

* add test for setting a different source directory

* use correct const for setting source dir property in tests

* import the AbstractPhpCodegen in test class

* put also Resources to source path

* save docs not to Resources

* update samples and improve src path in autoload.php and composer.json

* update moved samples

samples/server/petstore/php-symfony/SymfonyBundle-php/autoload.php

@@ -16,7 +16,7 @@
  *
  * After registering this autoload function with SPL, the following line
  * would cause the function to attempt to load the \OpenAPI\Server\Baz\Qux class
- * from /path/to/project/./Baz/Qux.php:
+ * from /path/to/project/Baz/Qux.php:
  *
  *      new \OpenAPI\Server\Baz\Qux;
  *
@@ -30,7 +30,7 @@ spl_autoload_register(function ($class) {
     $prefix = 'OpenAPI\\Server\\';
 
     // base directory for the namespace prefix
-    $base_dir = __DIR__ . '/./';
+    $base_dir = __DIR__ . '/';
 
     // does the class use the namespace prefix?
     $len = strlen($prefix);