Convert ANSI srting to utf-8 in arguments.

[mattn]

In non-English locales, we often search files with multi-byte strings. But Windows does not convert strings. If you prefer the way to use manifest file, I'll update this PR to switch the way.

    <windowsSettings>
      <activeCodePage xmlns="http://schemas.microsoft.com/SMI/2019/WindowsSettings">UTF-8</activeCodePage>
    </windowsSettings>

[k-takata]

Just FYI, I have enabled the UTF-8 mode in my Win32 builds using the following patch:
https://github.com/k-takata/the_silver_searcher-win32/blob/master/patches/0005-win32-Enable-UTF-8-mode-on-Windows-10-1903-or-later.patch