Function create_main_and_replica 

pub fn create_main_and_replica(
    locked: &mut Locked<Unlocked>,
    current_task: &CurrentTask,
    window_size: winsize,
) -> Result<(FileHandle, FileHandle), Errno>

Creates a terminal and returns the main pty and an associated replica pts.

This function assumes that /dev/ptmx is the DevPtmxFile and that devpts is mounted at /dev/pts. These assumptions are necessary so that the FileHandle objects returned have appropriate NamespaceNode objects.