[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/lgmp/CLGMPHost.h

@@ -0,0 +1,59 @@
+/**
+ * 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 <Windows.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+extern "C" {
+  #include "lgmp/host.h"
+}
+
+class CIVSHMEM;
+
+class CLGMPHost
+{
+private:
+  PLGMPHost m_host        = nullptr;
+  SRWLOCK   m_processLock = SRWLOCK_INIT;
+
+public:
+  CLGMPHost() = default;
+  ~CLGMPHost();
+
+  CLGMPHost(const CLGMPHost&) = delete;
+  CLGMPHost& operator=(const CLGMPHost&) = delete;
+
+  bool Initialize(CIVSHMEM& ivshmem);
+  void DeInit();
+
+  bool IsInitialized() const { return m_host != nullptr; }
+  LGMP_STATUS Process();
+
+  LGMP_STATUS CreateQueue(const struct LGMPQueueConfig& config,
+    PLGMPHostQueue * queue);
+  LGMP_STATUS Allocate(uint32_t size, PLGMPMemory * memory);
+  LGMP_STATUS AllocateAligned(uint32_t size, uint32_t alignment,
+    PLGMPMemory * memory);
+  size_t Available() const;
+};