Composing Getter & Optional returns lists

[kenbot]

get"$myObj.$lens.$optional" returns an Option, but get"$myObj.$getter.$optional" returns a List. This is because no "Fold1" exists, and a "Fold" is performed instead. This is surprising behaviour.

We can simulate the expected behaviour by tracking Folds that definitely only have 0-1 elements, and generating a .headOption on the end afterwards.

Something like:

case class Fold(notMulti: Boolean) extends OpticType

See optics-dev/Monocle#484

[kenbot]

"Fold1" added to OpticTypes, with appropriate composition rules.