cleo fails to detect ANSI support in Windows when run under a VT-native environment

[TBBle]

This is a replication of sdispater/clikit#35, as the faulty code moved from clikit to cleo.

The current final test of StreamOutput._has_color_support on Windows: https://github.com/sdispater/cleo/blob/7ebf50b4c85e0eca2d9f295588150527c95c84de/cleo/io/outputs/stream_output.py#L141-L147

returns False if ENABLE_VIRTUAL_TERMINAL_PROCESSING is already enabled, as is the case for Windows Terminal.

It should return True, since if ENABLE_VIRTUAL_TERMINAL_PROCESSING is already enabled, then we clearly have ANSI.

I suggest flipping the logic to look like

 if (mode.value & ENABLE_VIRTUAL_TERMINAL_PROCESSING) != 0: 
     return True

 return kernel32.SetConsoleMode( 
      h, mode.value | ENABLE_VIRTUAL_TERMINAL_PROCESSING 
  ) != 0

so that if ENABLE_VIRTUAL_TERMINAL_PROCESSING is already set, the output stream is seen as ANSI-enabled, and otherwise, only report ANSI-enabled if successfully able to change modes.

This also fixes the issue that the return value of kernel32.SetConsoleMode is not being checked, although I'm not aware of a situation that would reject that particular call.

The user-visible behaviour issue is python-poetry/poetry#3354