mtmd : Fix/Add non-ASCII file path support on Windows

[kuguma]

Summary

Fixed path handling in the mtmd feature on Windows to correctly convert and process non-ASCII file paths.

Additionally, fixed a missing console initialization in mtmd-cli.

Issues Resolved

• Failed to load .mmproj files with non-ASCII file paths

• Failed to load image files with non-ASCII file paths

• Incorrect path parsing in mtmd-cli when using /image <filepath> with non-ASCII characters

Comparison of behavior

Windows 11 Pro 24H2

PS > Get-WinSystemLocale
LCID             Name             DisplayName
----             ----             -----------
1041             ja-JP            Japanese (Japan)
PS > [Console]::InputEncoding.EncodingName
Japanese (Shift-JIS)
PS > [Console]::OutputEncoding.EncodingName
Unicode (UTF-8)

b6756

PS > llama-mtmd-cli.exe -m ... --mmproj ...
~~~
> /image テスト画像.jpg
Unable to open file ﾂテﾂスﾂトﾂ嘉ｦﾂ堕・jpg: Illegal byte sequence

This PR

PS > llama-mtmd-cli.exe -m ... --mmproj ...
~~~
> /image テスト画像.jpg
テスト画像.jpg image loaded

Notes

The general argument-handling logic in llama.cpp also has issues with non-ASCII paths.
Since the impact area is broad, I will submit a separate PR to address this.

[kuguma]

Fixed an unintended change in the PR.

[kuguma]

Hello, are there any remaining tasks to be done with the merge? Is there anything I can help with?

[ngxson]

superseded by #24779