Consider making list formatting closer to attrsets

[RuRo]

Description

Currently, lists are formatted quite differently compared to attrsets. I think, that most of the arguments for why attrsets are formatted the way they are, apply equally well to lists. Therefore, lists should be formatted in a way similar to attrsets.

Small example input

{
  attrset = { first = 1; second = 2; };

  list = [ "first = 1" "second = 2" ];

  longer_list_name = [ "this is" "a list that" "is barely longer" "than one line" ];
}

Expected output

{
  attrset = {
    first = 1;
    second = 2;
  };

  list = [
    "first = 1"
    "second = 2"
  ];

  longer_list_name = [
    "this is"
    "a list that"
    "is barely longer"
    "than one line"
  ];
}

Actual output

{
  attrset = {
    first = 1;
    second = 2;
  };

  list = [ "first = 1" "second = 2" ];

  longer_list_name =
    [ "this is" "a list that" "is barely longer" "than one line" ];
}

P.S. The ugly line break after longer_list_name = is actually a slightly more general problem that doesn't only affect lists, but also other elements that nixfmt doesn't "want"/know how to split. I'll be opening a separate issue for that problem shortly.

[piegamesde]

This should be fixed in #118