Merge branch '6.0' into 6.1

* 6.0:
  [BrowserKit] Merge fields and files recursively if they are multidimensional array
  [String] Fix `width` method in `AbstractUnicodeString`
  [Mailer] Add a comment to avoid the same wrong PR over and over again
  [Serializer] Fix XmlEncoder encoding attribute false
  [HttpFoundation] Fix `\Stringable` support in `InputBag::get()`

HttpBrowser.php

@@ -82,7 +82,7 @@ private function getBodyAndExtraHeaders(Request $request, array $headers): array
         $fields = $request->getParameters();
 
         if ($uploadedFiles = $this->getUploadedFiles($request->getFiles())) {
-            $part = new FormDataPart(array_merge($fields, $uploadedFiles));
+            $part = new FormDataPart(array_replace_recursive($fields, $uploadedFiles));
 
             return [$part->bodyToIterable(), $part->getPreparedHeaders()->toArray()];
         }

Tests/HttpBrowserTest.php

@@ -94,7 +94,11 @@ public function testMultiPartRequestWithSingleFile()
             ->with('POST', 'http://example.com/', $this->callback(function ($options) {
                 $this->assertStringContainsString('Content-Type: multipart/form-data', implode('', $options['headers']));
                 $this->assertInstanceOf(\Generator::class, $options['body']);
-                $this->assertStringContainsString('my_file', implode('', iterator_to_array($options['body'])));
+                $values = implode('', iterator_to_array($options['body'], false));
+                $this->assertStringContainsString('name="foo[file]"', $values);
+                $this->assertStringContainsString('my_file', $values);
+                $this->assertStringContainsString('name="foo[bar]"', $values);
+                $this->assertStringContainsString('foo2', $values);
 
                 return true;
             }))
@@ -103,7 +107,7 @@ public function testMultiPartRequestWithSingleFile()
         $browser = new HttpBrowser($client);
         $path = tempnam(sys_get_temp_dir(), 'http');
         file_put_contents($path, 'my_file');
-        $browser->request('POST', 'http://example.com/', [], ['file' => ['tmp_name' => $path, 'name' => 'foo']]);
+        $browser->request('POST', 'http://example.com/', ['foo' => ['bar' => 'foo2']], ['foo' => ['file' => ['tmp_name' => $path, 'name' => 'foo']]]);
     }
 
     public function testMultiPartRequestWithNormalFlatArray()