bug #40529 [Translation] Missing translations from traits (insekticid)

This PR was submitted for the 5.4 branch but it was merged into the 4.4 branch instead.

Discussion
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[Translation] Missing translations from traits

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #40528 <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

If you use ->trans() in traits, your translations will be cleaned with translation:update --clean command

Affected all Symfony versions

Please write some tests for me, I took me long time to debug and repair this :(

![image](https://user-images.githubusercontent.com/177340/111880657-159eac80-89ad-11eb-803b-7c63c67b27b9.png)

Commits
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0d8737ff16 Missing translations from traits

src/Symfony/Component/Translation/DependencyInjection/TranslatorPathsPass.php

@@ -60,6 +60,9 @@ class TranslatorPathsPass extends AbstractRecursivePass
             foreach ($this->paths as $class => $_) {
                 if (($r = $container->getReflectionClass($class)) && !$r->isInterface()) {
                     $paths[] = $r->getFileName();
+                    foreach ($r->getTraits() as $trait) {
+                        $paths[] = $trait->getFileName();
+                    }
                 }
             }
             if ($paths) {