[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/ITransport.h

@@ -0,0 +1,63 @@
+/**
+ * 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 "transport/FrameMemoryLimits.h"
+#include "transport/TransportTypes.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+class IControlTransport;
+class IFrameTransport;
+
+class ITransportEvents
+{
+public:
+  virtual ~ITransportEvents() = default;
+
+  virtual void OnSetCursorPos(int32_t x, int32_t y) = 0;
+  virtual void OnSetResolution(uint32_t width, uint32_t height) = 0;
+};
+
+class ITransport
+{
+public:
+  enum class OpenResult
+  {
+    SUCCESS,
+    RETRY,
+    FAILURE,
+  };
+
+  virtual ~ITransport() = default;
+
+  virtual OpenResult Open() = 0;
+  virtual bool Initialize() = 0;
+  virtual bool Setup(size_t alignment) = 0;
+  virtual void Process(ITransportEvents& events) = 0;
+
+  virtual FrameMemoryLimits GetMemoryLimits() const = 0;
+  virtual DirectFrameBufferMemory GetDirectMemory() const = 0;
+
+  virtual IFrameTransport& Frames() = 0;
+  virtual IControlTransport& Control() = 0;
+};