A type that gives one or more pieces of information, tagged with a path through a datastructure with fields and indices.
Most importantly, it is used for both Warnings and Errors in Json.Decode.Exploration.
Allows turning a non-empty list of Located a into a flat list of human
readable strings, provided we have a way to turn an a into some lines of text.
Each string represents a line. This allows arbitrary indentation by mapping over the lines and prepending some whitespace.