Make colored print handle UTF-8

[AlexGuteniev]

Fixes #2681

The working flow:

• With is_utf8() calls detail::print that specifically converts to UTF-16 and calls WriteConsoleW
• Without is_utf8() calls fwrite_fully

The broken flow:

• Always call fputs

The fix:

• With is_utf8() call detail::print
• Without is_utf8() keep calling fputs, as fwrite_fully is not exported

This is tested on Windows only. On Windows fputs does not do any magic, and color sequences are processed by WriteConsole. I'm not sure if on other platform fputs processes these ANSI escape sequences, or fwrite will also do.

[AlexGuteniev]

I actually observe inconsistency that non-colored format throws I/O errors but colored directly calls fputs without checking. I'm not creating the issue yet, maybe it should be fixed within this change.

[vitaut]

Thanks for the PR!

I actually observe inconsistency that non-colored format throws I/O errors but colored directly calls fputs without checking. I'm not creating the issue yet, maybe it should be fixed within this change.

Good catch, please add an error check here or in a separate PR.