refactor into files

src/main/cpp/assets_manager.h

@@ -0,0 +1,12 @@
+#pragma once
+#include <vector>
+
+struct AAssetManager;
+
+class AssetsManager
+{
+    static inline AAssetManager* m_asset_manager = nullptr;
+public:
+    static void Init(AAssetManager* asset_manager);
+    static std::vector<uint8_t> ReadAll(const std::string& filename);
+};