windows: replace Win32 MBS conversions with WTF-8 (#60605)
Replace all WideCharToMultiByte/MultiByteToWideChar API calls with WTF-8
based conversions using libuv helpers (uv_utf16_to_wtf8,
uv_wtf8_to_utf16, etc.) in the runtime, and a standalone copy of the
libuv algorithm in the CLI loader.
Refs #33486
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
