minor #13060 [2.7] adds deprecation notices. (hhamon)

This PR was merged into the 2.7 branch.

Discussion
----------

[2.7] adds deprecation notices.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #12608, #12672, #12675 #12684, #12686
| License       | MIT
| Doc PR        | ~

Commits
-------

f9fbb4f Fixes more deprecation notices as per @stof review.
fd47c07 Fixed some deprecations according to @stof feedbacks.
2a3e7d2 Normalizes deprecation notice messages.
738b9be [Validator] fixes UuidValidator deprecated class namespace.
e608ba6 [Form] adds more deprecation notices.
cd9617a [Validator] adds more deprecation notices.
a7f841e [Form] Adds a way to trigger deprecation notice on demand for VirtualFormAwareIterator class.
97efd2c Fixes more deprecation notices.
fd9c7bb Normalized @deprecated annotations.
39cfd47 Removed deprecation notices from test files.
2a9749d Fixes deprecation notices.
6f57b7b Reverted trigger_error() function calls on deprecated interfaces to prevent breaking third party projects implementing them.
86b9f6b Adds deprecation notices for structures to be removed in 3.0.

Author: fabpot

Session/Flash/FlashBag.php

@@ -169,12 +169,14 @@ public function clear()
     /**
      * Returns an iterator for flashes.
      *
-     * @deprecated Will be removed in 3.0.
+     * @deprecated since version 2.4, to be removed in 3.0.
      *
      * @return \ArrayIterator An \ArrayIterator instance
      */
     public function getIterator()
     {
+        trigger_error('The '.__METHOD__.' method is deprecated since version 2.4 and will be removed in 3.0.', E_USER_DEPRECATED);
+
         return new \ArrayIterator($this->all());
     }
 }

Session/Storage/Handler/LegacyPdoSessionHandler.php

@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\HttpFoundation\Session\Storage\Handler;
 
+trigger_error('The '.__NAMESPACE__.'\LegacyPdoSessionHandler class is deprecated since version 2.6 and will be removed in 3.0. Use the Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler class instead.', E_USER_DEPRECATED);
+
 /**
  * Session handler using a PDO connection to read and write data.
  *
@@ -24,7 +26,7 @@
  * @author Michael Williams <michael.williams@funsational.com>
  * @author Tobias Schultze <http://tobion.de>
  *
- * @deprecated Deprecated since version 2.6, to be removed in 3.0. Use
+ * @deprecated since version 2.6, to be removed in 3.0. Use
  *             {@link PdoSessionHandler} instead.
  */
 class LegacyPdoSessionHandler implements \SessionHandlerInterface
@@ -77,8 +79,6 @@ public function __construct(\PDO $pdo, array $dbOptions = array())
             throw new \InvalidArgumentException(sprintf('"%s" requires PDO error mode attribute be set to throw Exceptions (i.e. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION))', __CLASS__));
         }
 
-        trigger_error('"Symfony\Component\HttpFoundation\Session\Storage\Handler\LegacyPdoSessionHandler" is deprecated since version 2.6 and will be removed in 3.0. Use "Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler" instead.', E_USER_DEPRECATED);
-
         $this->pdo = $pdo;
         $dbOptions = array_merge(array(
             'db_id_col' => 'sess_id',