Bug: On Windows, Unicode file name not supported by tex binaries

[ttk at t-lab.opal.ne.jp]

Thank you for your reports and helpful discussion.

I have confirmed the error with plain tex inputs on Msys2 mingw64, Windows 11.
However, the results were found also on Windows Subsystem for Linux (Ubuntu).

engine:
(A) pdftex -ini -interaction nonstopmode -jobname=foo BananaXXX.tex
(B) euptex -ini -interaction nonstopmode -jobname=foo BananaXXX.tex
(C) xetex -ini -interaction nonstopmode -jobname=foo BananaXXX.tex

file name:
(1) Bananaбанан.tex (2byte UTF-8)
(2) Bananaバナナ.tex (3byte UTF-8)
(3) Banana🍌.tex (4byte UTF-8)

The input file is plain tex with UTF-8 text ::
```
\catcode`\{=1
\catcode`\}=2
\immediate\write16{Bananaбананバナナ🍌}
\end
```

The results on my environment (both Msys2, WSL)
(A) : OK for (1)(2)(3)
(B) : OK for (1)(2)(3)
(C) : OK for (1)(2), fail for (3)

The treatment of Unicode file name on Windows are very different from that of Linux.
However, the error seems not caused by the difference.
More study is required.

Best,
Takuji Tanaka