Ladybird: Use QtNetwork for HTTP and HTTPS requests

Until we can get our own RequestServer infrastructure up and running,
running the TLS and HTTP code in-process was causing lots of crashes
due to unexpected reentrancy via nested event loops.

This patch adds a simple backend for HTTP and HTTPS requests that simply
funnels them through QNetworkAccessManager.

Ladybird/RequestManagerQt.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#define AK_DONT_REPLACE_STD
+
+#include <LibWeb/Loader/ResourceLoader.h>
+#include <QtNetwork/QNetworkAccessManager>
+#include <QtNetwork/QNetworkReply>
+
+class RequestManagerQt
+    : public QObject
+    , public Web::ResourceLoaderConnector {
+    Q_OBJECT
+public:
+    static NonnullRefPtr<RequestManagerQt> create()
+    {
+        return adopt_ref(*new RequestManagerQt());
+    }
+
+    virtual ~RequestManagerQt() override { }
+
+    virtual void prefetch_dns(AK::URL const&) override { }
+    virtual void preconnect(AK::URL const&) override { }
+
+    virtual RefPtr<Web::ResourceLoaderConnectorRequest> start_request(String const& method, AK::URL const&, HashMap<String, String> const& request_headers, ReadonlyBytes request_body, Core::ProxyData const&) override;
+
+private slots:
+    void reply_finished(QNetworkReply*);
+
+private:
+    RequestManagerQt();
+
+    class Request
+        : public Web::ResourceLoaderConnectorRequest {
+    public:
+        static ErrorOr<NonnullRefPtr<Request>> create(QNetworkAccessManager& qnam, String const& method, AK::URL const& url, HashMap<String, String> const& request_headers, ReadonlyBytes request_body, Core::ProxyData const&);
+
+        virtual ~Request() override;
+
+        virtual void set_should_buffer_all_input(bool) override { }
+        virtual bool stop() override { return false; }
+        virtual void stream_into(Core::Stream::Stream&) override { }
+
+        void did_finish();
+
+        QNetworkReply& reply() { return m_reply; }
+
+    private:
+        Request(QNetworkReply&);
+
+        QNetworkReply& m_reply;
+    };
+
+    HashMap<QNetworkReply*, NonnullRefPtr<Request>> m_pending;
+    QNetworkAccessManager* m_qnam { nullptr };
+};