Use OpenSSL for ECDH during client login, drop mdanter/ecc (#4328)

This brings a significant performance improvement to login sequence handling, reducing CPU cost of `PrepareEncryptionTask` by over 90% and `ProcessLoginTask` by over 60%. It also allows us to shed a dependency.

tests/phpstan/stubs/phpasn1.stub

@@ -0,0 +1,22 @@
+<?php
+/*
+ * This file is part of the PHPASN1 library.
+ *
+ * Copyright © Friedrich Große <friedrich.grosse@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FG\ASN1\Universal;
+
+class Integer
+{
+    /**
+     * @param int|string $value
+     */
+    public function __construct($value){}
+
+    /** @return int|string */
+    public function getContent(){}
+}