[camera][draft] Add camera plugin (#29)

Added the first draft version, but there are still a lot of unimplemented features.

packages/camera/elinux/include/camera_elinux/camera_elinux_plugin.h

@@ -0,0 +1,23 @@
+#ifndef FLUTTER_PLUGIN_CAMERA_CAMERA_ELINUX_PLUGIN_H_
+#define FLUTTER_PLUGIN_CAMERA_CAMERA_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 CameraElinuxPluginRegisterWithRegistrar(
+    FlutterDesktopPluginRegistrarRef registrar);
+
+#if defined(__cplusplus)
+}  // extern "C"
+#endif
+
+#endif  // FLUTTER_PLUGIN_CAMERA_CAMERA_ELINUX_PLUGIN_H_