Windows symlink oddness

This simple test fails on Windows:

```rust
use std::process;
extern crate wit_bindgen;

wit_bindgen::generate!({
inline: r"
package test:test;

world test {
include wasi:filesystem/imports@0.3.0-rc-2025-09-16;
include wasi:cli/command@0.3.0-rc-2025-09-16;
}
",
additional_derives: [PartialEq, Eq, Hash, Clone],
// Work around https://github.com/bytecodealliance/wasm-tools/issues/2285.
features:["clocks-timezone"],
generate_all
});

async fn test_symlink() {
match &wasi::filesystem::preopens::get_directories()[..] {
[(dir, _)] => {
dir.symlink_at("..".to_string(), "t".to_string())
.await
.unwrap();
dir.unlink_file_at("t".to_string()).await.unwrap();
}
[..] => {
eprintln!("usage: run with one open dir");
process::exit(1)
}
}
}

struct Component;
export!(Component);
impl exports::wasi::cli::run::Guest for Component {
async fn run() -> Result<(), ()> {
test_symlink().await;
Ok(())
}
}

fn main() {
unreachable!("main is a stub");
}
```

The issue is that creating a symlink to `..` doesn't work and fails with `EPERM`, whereas on POSIX platforms any permission check is only made when dereferencing the symlink.

Similarly, `ln_s("does-not-exist".to_string(), "whatever".to_string).await.unwrap()` fails on Windows with `ENOENT`. I can make a symlink to a file that does exist, however. I only tested via CI, on https://github.com/WebAssembly/wasi-testsuite/pull/195.

What's going on? Is this another area of WASI in which we have to relax the requirements?