On Windows, the only reliable way to read/write Unicode text from/to a
Console is to use `ReadConsoleW` and `WriteConsoleW` and convert from/to
wide-character encoding. When `cin`, `cout`, and/or `cerr` are attached
to a Windows Console, use a custom C++ `streambuf` to handle the I/O.
This will replace KWSys ConsoleBuf, whose implementation is more complex
to support narrow output streams on Windows non-UTF-8 narrow encodings.
We only need to support UTF-8.
Issue: #26924
