gh-85984: New additions and improvements to the tty library. (#101832)

New additions to the tty library. Functions added: cfmakeraw(), and cfmakecbreak(). The
functions setcbreak() and setraw() now return original termios to save an extra tcgetattr() call.

---------

Signed-off-by: Soumendra Ganguly <soumendraganguly@gmail.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Gregory P. Smith [Google LLC] <greg@krypto.org>