CLI option to format non-singleton lists on one line

[MattSturgeon]

Description

In the same spirit as --width (default 100) allowing end-users outside of nixpkgs to tweak nixfmt's behavior, I'd like an option to disable the default formatting of non-singleton lists.

When the option is enabled, lists of any element count should be rendered on a single line unless that cannot be done for some other reason, such as comments within the list or the total line length being too long.

Better yet, a granular --max-list-items option could be added:

• default 1 for the current behavior
• 0 would always produce a multi-line list
• a negative value (-1) would always produce a single-line list (if possible, as described in the rest of this issue).
• Any other positive integer would use that value as the threshold for when to no longer attempt to format a list on a single line.

Small example input

{
  single = ["a"];
  short = ["a" "b" "c"];
  long = ["a very very" "long list of" "a few elements" "with many many" "characters!"];
  shortWithComment = [
    # Elements
    "a" "b" "c"
  ];
  shortListWithAVeryVeryLongName_LoremipsumdolorsitametconsecteturadipiscingelitPhasellusaliquetutmauriseumollisSuspendisserhoncusdui = ["a" "b" "c"];
}

Expected output

{
  single = [ "a" ];
  short = [ "a" "b" "c" ];
  long = [
    "a very very"
    "long list of"
    "a few elements"
    "with many many"
    "characters!"
  ];
  shortWithComment = [
    # Elements
    "a"
    "b"
    "c"
  ];
  shortListWithAVeryVeryLongName_LoremipsumdolorsitametconsecteturadipiscingelitPhasellusaliquetutmauriseumollisSuspendisserhoncusdui =
    [ "a" "b" "c" ];
}

Actual output

{
  single = [ "a" ];
  short = [
    "a"
    "b"
    "c"
  ];
  long = [
    "a very very"
    "long list of"
    "a few elements"
    "with many many"
    "characters!"
  ];
  shortWithComment = [
    # Elements
    "a"
    "b"
    "c"
  ];
  shortListWithAVeryVeryLongName_LoremipsumdolorsitametconsecteturadipiscingelitPhasellusaliquetutmauriseumollisSuspendisserhoncusdui = [
    "a"
    "b"
    "c"
  ];

Note: Only the short list and the short list with a long name should be formatted differently when --single-line-lists is used.

Related

This is essentially the opposite of #136 which was asking to revert https://github.com/NixOS/nixfmt/commit/d2e8575db66eac5252323b352e3e1b14a2a1646e