Optimize println() overloads added in P3142R0

[frederick-vs-ja]

Fixes #4630.

• Add a function __std_print_newline_only_to_unicode_console to the import library to avoid potential branches around WriteConsoleW.
• Use sputc for non-Unicode new line printing for ostream to reduce potential branches.
• Use fputc for non-Unicode new line printing for FILE* as the function seems to be the simplest for the purpose in UCRT.

[StephanTLavavej]

Thanks! 😻 I pushed a conflict-free merge with main followed by several refactorings, shrinking the diff from +181 -2 to +115 -10. Originally, this PR looked like it was adding significant complexity, but now I like where it ended up. I'd still like @CaseyCarter to look at this.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for figuring out the surprisingly complicated logic needed to make these functions fast! 🚀 😻 💚