Merge branch '5.4' into 6.0

* 5.4:
  fix SQLSRV throws for method_exists()
  [HttpKernel] Add basic support for language negotiation
  [Messenger] Add a middleware to log when transaction has been left open
  [HttpClient] Add method to set response factory in mock client
  Move array_merge calls out of loops to improve performance
  Remove references to DBALException
  [VarDumper] Fix handling of "new" in initializers on PHP 8.1

Author: derrabus

DebugClassLoader.php

@@ -803,7 +803,7 @@ private function setReturnType(string $types, string $class, string $method, str
                 continue;
             }
 
-            $docTypes = array_merge($docTypes, $t);
+            $docTypes[] = $t;
 
             if ('mixed' === $n || 'void' === $n) {
                 $nullable = false;
@@ -820,6 +820,7 @@ private function setReturnType(string $types, string $class, string $method, str
                 $phpTypes[] = $n;
             }
         }
+        $docTypes = array_merge([], ...$docTypes);
 
         if (!$phpTypes) {
             return;

ErrorEnhancer/ClassNotFoundErrorEnhancer.php

@@ -93,19 +93,19 @@ private function getClassCandidates(string $class): array
             if ($function[0] instanceof ClassLoader) {
                 foreach ($function[0]->getPrefixes() as $prefix => $paths) {
                     foreach ($paths as $path) {
-                        $classes = array_merge($classes, $this->findClassInPath($path, $class, $prefix));
+                        $classes[] = $this->findClassInPath($path, $class, $prefix);
                     }
                 }
 
                 foreach ($function[0]->getPrefixesPsr4() as $prefix => $paths) {
                     foreach ($paths as $path) {
-                        $classes = array_merge($classes, $this->findClassInPath($path, $class, $prefix));
+                        $classes[] = $this->findClassInPath($path, $class, $prefix);
                     }
                 }
             }
         }
 
-        return array_unique($classes);
+        return array_unique(array_merge([], ...$classes));
     }
 
     private function findClassInPath(string $path, string $class, string $prefix): array