fix(ext/fs): surface non-UTF-8 file names from read_dir (#34623)

## Summary

`read_dir` in `ext/fs/std_fs.rs` previously dropped any directory entry
whose name was not valid UTF-8 (`OsString::into_string().ok()?`). That
silent filter made files with non-UTF-8 names invisible to
`node:fs.globSync`, `node:fs.readdirSync`, and `Deno.readDirSync` — so
the bug report at #30873 (`fs.globSync returns incorrect results with
non-UTF8 encoded file names`) was actually two problems stacked:

1. The file existed on disk, but `read_dir` silently skipped it.
2. The user's own `writeFileSync(Buffer.from([0xe9]), 'hello')` lossily
encoded the Buffer path to `�` (UTF-8 `EF BF BD`) before reaching the
open syscall, so the file that *did* show up was actually a different,
valid-UTF-8-named file.

This PR fixes problem (1). Switching to `to_string_lossy().into_owned()`
keeps the entry in the listing, with invalid byte sequences replaced by
U+FFFD — matching Node's default `utf8` readdir behavior. (Lossless
Buffer-path support throughout the fs ops is a larger refactor, separate
from this regression.)

## Test plan

- [x] Added regression test `[node/fs globSync] surfaces files with
non-UTF-8 names` (Linux only — macOS/Windows reject or normalize
non-UTF-8 names at the filesystem layer). The fixture is built via `bash
+ printf` so the raw `0xE9` byte reaches the kernel unmolested.
- [ ] CI green on Linux/macOS/Windows.

Closes denoland/divybot#376

Co-authored-by: divybot <divybot@users.noreply.github.com>
Co-authored-by: Divy Srivastava <me@littledivy.com>