minor #12750 [Hackday] - add trigger error for deprecated clases. (desarrolla2)

This PR was squashed before being merged into the 2.7 branch (closes #12750).

Discussion
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[Hackday] - add trigger error for deprecated clases.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | #12669
| License       | MIT
| Doc PR        | -

Commits
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48dd497 [Hackday] - add trigger error for deprecated clases.

Author: fabpot

Constraints/Collection/Optional.php

@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\Validator\Constraints\Collection;
 
+trigger_error('Symfony\Component\Validator\Constraints\Collection\Optional was deprecated in version 2.3 and will be removed in 3.0. You should use Symfony\Component\Validator\Constraints\Optional instead.', E_USER_DEPRECATED);
+
 use Symfony\Component\Validator\Constraints\Optional as BaseOptional;
 
 /**

Constraints/Collection/Required.php

@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\Validator\Constraints\Collection;
 
+trigger_error('Symfony\Component\Validator\Constraints\Collection\Required was deprecated in version 2.3 and will be removed in 3.0. You should use Symfony\Component\Validator\Constraints\Required instead.', E_USER_DEPRECATED);
+
 use Symfony\Component\Validator\Constraints\Required as BaseRequired;
 
 /**