refactor: Replace fs::unique_path with GetUniquePath(path) calls #21052

This PR makes it easier in #20744 to remove our dependency on the boost::filesystem::unique_path() function which does not have a direct equivalent in C++17.

This PR attempts to re-implement boost::filesystem::unique_path() as GetUniquePath(path) but the implementations are not meant to be the same.

Note:

• Boost 1.75.0 implementation of unique_path: https://github.com/boostorg/filesystem/blob/9cab675b71e98706886a87afe7c19eb9da568961/src/unique_path.cpp#L235

• In the previous implementation, I attempted to add:

  fs::path GetUniquePath(const fs::path& base)
  {
      FastRandomContext rnd;
      fs::path tmpFile = base / HexStr(rnd.randbytes(8));
      return tmpFile;
  }
  

  to fs.cpp but this leads to a circular dependency: "fs -> random -> logging -> fs". That is why the modified implementation adds a new file.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #20744 ([POC] Use std::filesystem. Remove Boost Filesystem & System by fanquake)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Concept ACK

However, this introduces a circular dependency right now:

A new circular dependency in the form of "fs -> random -> logging -> fs" appears to have been introduced.

However, this introduces a circular dependency right now:

I have changed the implementation. So this is fixed.

Concept ACK

Thanks for paving the way for further Boost removal!

Code review ACK 1bca2aa694cd85984c09699ae28daec313077462. It's a simple change and extra test coverage is nice

Code review ACK 1bca2aa694cd85984c09699ae28daec313077462