Add video player (#2)

https://github.com/sony/flutter-embedded-linux/issues/124

packages/video_player/elinux/include/video_player_elinux/video_player_elinux_plugin.h

@@ -0,0 +1,23 @@
+#ifndef FLUTTER_PLUGIN_VIDEO_PLAYER_ELINUX_PLUGIN_H_
+#define FLUTTER_PLUGIN_VIDEO_PLAYER_ELINUX_PLUGIN_H_
+
+#include <flutter_plugin_registrar.h>
+
+#ifdef FLUTTER_PLUGIN_IMPL
+#define FLUTTER_PLUGIN_EXPORT __attribute__((visibility("default")))
+#else
+#define FLUTTER_PLUGIN_EXPORT
+#endif
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+FLUTTER_PLUGIN_EXPORT void VideoPlayerElinuxPluginRegisterWithRegistrar(
+    FlutterDesktopPluginRegistrarRef registrar);
+
+#if defined(__cplusplus)
+}  // extern "C"
+#endif
+
+#endif  // FLUTTER_PLUGIN_VIDEO_PLAYER_ELINUX_PLUGIN_H_