minor #21676 [Serializer] Reduce complexity of NameConverter (gadelat)

This PR was merged into the 3.3-dev branch.

Discussion
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[Serializer] Reduce complexity of NameConverter

Cleaner and faster implementation of camelcase normalization.
Speed improvement is particularly visible in long string input.

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

Commits
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50ca944 [Serializer] Reduce complexity of NameConverter

Author: fabpot

src/Symfony/Component/Serializer/NameConverter/CamelCaseToSnakeCaseNameConverter.php

@@ -44,19 +44,7 @@ public function __construct(array $attributes = null, $lowerCamelCase = true)
     public function normalize($propertyName)
     {
         if (null === $this->attributes || in_array($propertyName, $this->attributes)) {
-            $lcPropertyName = lcfirst($propertyName);
-            $snakeCasedName = '';
-
-            $len = strlen($lcPropertyName);
-            for ($i = 0; $i < $len; ++$i) {
-                if (ctype_upper($lcPropertyName[$i])) {
-                    $snakeCasedName .= '_'.strtolower($lcPropertyName[$i]);
-                } else {
-                    $snakeCasedName .= strtolower($lcPropertyName[$i]);
-                }
-            }
-
-            return $snakeCasedName;
+            return strtolower(preg_replace('/[A-Z]/', '_\\0', lcfirst($propertyName)));
         }
 
         return $propertyName;