LibCodeComprehension: Re-organize code comprehension related code

This moves all code comprehension-related code to a new library,
LibCodeComprehension.

This also moves some types related to code comprehension tasks (such as
autocomplete, find declaration) out of LibGUI and into
LibCodeComprehension.

Userland/Libraries/LibCodeComprehension/Shell/main.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "ConnectionFromClient.h"
+#include <LibCore/EventLoop.h>
+#include <LibCore/LocalServer.h>
+#include <LibCore/System.h>
+#include <LibIPC/SingleServer.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments)
+{
+    Core::EventLoop event_loop;
+    TRY(Core::System::pledge("stdio unix rpath recvfd"));
+
+    auto client = TRY(IPC::take_over_accepted_client_from_system_server<LanguageServers::Shell::ConnectionFromClient>());
+
+    TRY(Core::System::pledge("stdio rpath recvfd"));
+    TRY(Core::System::unveil("/etc/passwd", "r"));
+
+    return event_loop.exec();
+}