LibGUI: Add GTCPSocket and base class GSocket (inherits from GIODevice.)

And use these to do the line-by-line reading automagically instead of having
that logic in IRCClient. This will definitely come in handy.

LibGUI/GSocket.h

@@ -0,0 +1,68 @@
+#pragma once
+
+#include <LibGUI/GIODevice.h>
+#include <AK/AKString.h>
+#include <Kernel/IPv4.h>
+
+class GSocketAddress {
+public:
+    enum class Type { Invalid, IPv4, Local };
+
+    GSocketAddress() { }
+    GSocketAddress(const IPv4Address& address)
+        : m_type(Type::IPv4)
+        , m_ipv4_address(address)
+    {
+    }
+
+    Type type() const { return m_type; }
+    bool is_valid() const { return m_type != Type::Invalid; }
+    IPv4Address ipv4_address() const { return m_ipv4_address; }
+
+    String to_string() const
+    {
+        switch (m_type) {
+        case Type::IPv4: return m_ipv4_address.to_string();
+        default: return "[GSocketAddress]";
+        }
+    }
+
+private:
+    Type m_type { Type::Invalid };
+    IPv4Address m_ipv4_address;
+};
+
+class GSocket : public GIODevice {
+public:
+    enum class Type { Invalid, TCP, UDP };
+    virtual ~GSocket() override;
+
+    bool connect(const GSocketAddress&, int port);
+
+    ByteBuffer receive(int max_size);
+    bool send(const ByteBuffer&);
+
+    bool is_connected() const { return m_connected; }
+
+    GSocketAddress source_address() const { return m_source_address; }
+    int source_port() const { return m_source_port; }
+
+    GSocketAddress destination_address() const { return m_source_address; }
+    int destination_port() const { return m_destination_port; }
+
+    virtual const char* class_name() const override { return "GSocket"; }
+
+protected:
+    GSocket(Type, GObject* parent);
+
+    GSocketAddress m_source_address;
+    GSocketAddress m_destination_address;
+    int m_source_port { -1 };
+    int m_destination_port { -1 };
+    bool m_connected { false };
+
+private:
+    virtual bool open(GIODevice::OpenMode) override { ASSERT_NOT_REACHED(); }
+    Type m_type { Type::Invalid };
+
+};