[HttpFoundation] Emit PHP warning when Response::sendHeaders() while output has already been sent

Author: ivo95v

Response.php

@@ -317,6 +317,11 @@ public function sendHeaders(?int $statusCode = null): static
     {
         // headers have already been sent by the developer
         if (headers_sent()) {
+            if (!\in_array(\PHP_SAPI, ['cli', 'phpdbg', 'embed'], true)) {
+                $statusCode ??= $this->statusCode;
+                header(\sprintf('HTTP/%s %s %s', $this->version, $statusCode, $this->statusText), true, $statusCode);
+            }
+
             return $this;
         }