Optimize reading lines with `Newline::kLfOrCrLf`: search for only LF first, then look back if it was preceded by CR, instead of checking for either CR or LF at each character.
Optimize reading lines with `Newline::kLfOrCrLf`: search for only LF first, then
look back if it was preceded by CR, instead of checking for either CR or LF at
each character.

PiperOrigin-RevId: 489246731

google/riegeli,google/riegeli,google/riegeli,google/riegeli