LibIPC+LibGfx: Templatize IPC encoding as well as decoding

Now most classes dictate how they are serialized and deserialized when
transmitted across LibIPC sockets. This also makes the IPC compiler
a bit simpler. :^)

Libraries/LibIPC/Encoder.h

@@ -31,6 +31,13 @@
 
 namespace IPC {
 
+template<typename T>
+bool encode(BufferStream&, T&)
+{
+    ASSERT_NOT_REACHED();
+    return false;
+}
+
 class Encoder {
 public:
     explicit Encoder(MessageBuffer& buffer)
@@ -53,6 +60,28 @@ public:
     Encoder& operator<<(const String&);
     Encoder& operator<<(const Dictionary&);
 
+    template<typename T>
+    Encoder& operator<<(const Vector<T>& vector)
+    {
+        *this << (u64)vector.size();
+        for (auto& value : vector)
+            *this << value;
+        return *this;
+    }
+
+    template<typename T>
+    Encoder& operator<<(const T& value)
+    {
+        encode(value);
+        return *this;
+    }
+
+    template<typename T>
+    void encode(const T& value)
+    {
+        IPC::encode(*this, value);
+    }
+
 private:
     MessageBuffer& m_buffer;
 };