LibWeb+WebContent: Spawn Worker processes from the chrome

Instead of spawning these processes from the WebContent process, we now
create them in the Browser chrome.

Part 1/N of "all processes are owned by the chrome".

Userland/Libraries/LibWebView/SocketPair.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2024, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibIPC/File.h>
+
+namespace WebView {
+
+struct SocketPair {
+    IPC::File socket;
+    IPC::File fd_passing_socket;
+};
+
+}
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(Encoder&, WebView::SocketPair const&);
+
+template<>
+ErrorOr<WebView::SocketPair> decode(Decoder&);
+
+}