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/LibGfx/Size.cpp

@@ -28,6 +28,7 @@
 #include <AK/String.h>
 #include <LibGfx/Size.h>
 #include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
 
 namespace Gfx {
 
@@ -45,6 +46,12 @@ const LogStream& operator<<(const LogStream& stream, const Size& value)
 
 namespace IPC {
 
+bool encode(Encoder& encoder, const Gfx::Size& size)
+{
+    encoder << size.width() << size.height();
+    return true;
+}
+
 bool decode(Decoder& decoder, Gfx::Size& size)
 {
     int width = 0;