Add the renderer process

The renderer becomes two programs: the adapter (t5deRenderEngine.dll, 32-bit, in IMVU's process) and a 64-bit renderer process (t5de-renderer.exe) drawing with Diligent Engine, fetched with FetchContent and pinned. For now a spike: the adapter starts the renderer process for each engine and signals each frame through a shared memory channel, and the renderer process draws a box into a child window in the client's 3D view.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

adapter/plugin.def

@@ -0,0 +1,5 @@
+; The names SceneWindow.dll's createDLLRenderer looks up, without C++ or __cdecl decoration.
+LIBRARY t5deRenderEngine
+EXPORTS
+    isRenderEngineSupported
+    createRenderEngine