Deprecate some of LLAPRFile fulnctions

[akleshchev]

LLAPRFile is old and crashy. Use newer std filesystem where possible.

---

This repo is using Opire - what does it mean? 👇

💵 Everyone can add rewards for this issue commenting /reward 100 (replace 100 with the amount).
🕵️‍♂️ If someone starts working on this issue to earn the rewards, they can comment /try to let everyone know!
🙌 And when they open the PR, they can comment /claim #5067 either in the PR description or in a PR's comment.

🪙 Also, everyone can tip any user commenting /tip 20 @akleshchev (replace 20 with the amount, and @akleshchev with the user to tip).

📖 If you want to learn more, check out our documentation.