This allows us to have newline not affect the wrap status of a line.
Now a lines wrapping status is changed only when the last cell
in the line is changed. This actually matches the behavior of many other
terminal emulators so is probably a good thing from a ecosystem
compatibility perspective.
The fish shell expects this weird behavior of newline not changing
wrapping status, for unknown reasons, which is the actual motivation for
doing all this work.
Fixes#5766
68cf9f7514