[idd] transport: abstract LGMP implementation

Introduce transport, frame, and control interfaces with an LGMP factory
backend.

Move LGMP and IVSHMEM implementation details under transport/lgmp and
expose direct frame-buffer memory through a neutral capability.

idd/LGIdd/transport/IControlTransport.h

@@ -0,0 +1,42 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#pragma once
+
+#include "postprocess/D12FrameFormat.h"
+
+#include <Windows.h>
+#include <wdf.h>
+#include <IddCx.h>
+
+#include <memory>
+
+class IControlTransport
+{
+public:
+  virtual ~IControlTransport() = default;
+
+  virtual void SendCursor(const IDARG_OUT_QUERY_HWCURSOR& info,
+    const BYTE * data, UINT sdrWhiteLevel) = 0;
+  virtual void SetColorTransform(
+    std::shared_ptr<const D12ColorTransform> transform) = 0;
+  virtual std::shared_ptr<const D12ColorTransform>
+    GetColorTransform() const = 0;
+};