LibCore: Add CTCPServer

This is pretty much a find/replace copy of CLocalServer, and some
modifications to CTCPSocket and CSocketAddress to support it.

Libraries/LibCore/CTCPServer.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <AK/IPv4Address.h>
+#include <LibCore/CNotifier.h>
+#include <LibCore/CObject.h>
+
+class CTCPSocket;
+
+class CTCPServer : public CObject {
+    C_OBJECT(CTCPServer)
+public:
+    explicit CTCPServer(CObject* parent = nullptr);
+    virtual ~CTCPServer() override;
+
+    bool is_listening() const { return m_listening; }
+    bool listen(const IPv4Address& address, u16 port);
+
+    CTCPSocket* accept();
+
+    Function<void()> on_ready_to_accept;
+
+private:
+    int m_fd { -1 };
+    bool m_listening { false };
+    OwnPtr<CNotifier> m_notifier;
+};