[hl] sys.FileSystem.exists(...) always returns `true` on MacOS for non-existing files

The code
```haxe
trace(sys.FileSystem.exists("non-existing-file.txt"));
```
always returns `true` on MacOS with HashLink 1.13. It works fine on Windows and Linux.

I tried with Haxe 4.2.5 and the latest Haxe development build.

```sh
bash-3.2$ uname -a
Darwin Mac-1676552967785.local 21.6.0 Darwin Kernel Version 21.6.0: Mon Dec 19 20:44:01 PST 2022; root:xnu-8020.240.18~2/RELEASE_X86_64 x86_64

bash-3.2$ echo $OSTYPE
darwin21
```

@ncannasse is there any possible workaround?

Start by locating the HashLink 1.13 implementation of sys.FileSystem.exists for macOS and compare it with the Windows and Linux implementations. Run the provided Haxe example on macOS to reproduce the result; done means a nonexistent file returns false consistently on macOS.

Written by the indexing model from the issue text.