refactor Windows classes to separate EGL/WGL/Backing Window

windows/flutter_texture_buffer.h

@@ -0,0 +1,18 @@
+#ifndef _FLUTTER_TEXTURE_BUFFER_H
+#define _FLUTTER_TEXTURE_BUFFER_H
+
+#include <flutter/method_channel.h>
+#include <flutter/plugin_registrar_windows.h>
+#include <flutter/standard_method_codec.h>
+#include <flutter/texture_registrar.h>
+
+
+namespace polyvox_filament {
+
+    class FlutterTextureBuffer {
+    public:
+        int64_t flutterTextureId = 0;
+    };
+}
+
+#endif