typechecker: target line-clear term sequences to ttys only

Summary: * ensure that the line-clearing command is not invoked with any ##--from##
 * line-clearing ansi sequence is private to the module; \n should be used for non-tty
 * renamed ttyColor.ml to tty.ml, since it houses other functionality
 * moved tty-related code from utils.ml to tty.ml

Reviewed By: @pikatchu

Differential Revision: D1426336