Format: fix indent of nested array elements

[makenowjust]

Fixed #7443

With more precision, this change treats multiline elements.
This change detects multiline elenent and keeps current indent in this case, or elements will be aligned at start column.

Now, the formatter keeps these formats:

# #7048
[
  {
    "some" => "hash",
    "with" => "values",
  }, {
    "another"  => "hash",
    "will get" => "deindented",
  }, {
    "now" => "totally",
  }, {
    "flat" => "against the left",
  },
]

# #7443
very_long_variable_name = [{
  :foo => :bar,
}]

very_long_variable_name = [
  {
    :foo => :bar,
  }, {
    :bar => :baz,
  },
]

very_long_variable_name = [
  {
    :foo => :bar,
  },
  {
    :bar => :baz,
  },
]

# single-line elements case

foo = [1, 2, 3,
       4, 5, 6]

foo = [1, 2, 3, # foo
       4, 5, 6]

foo = [
  1, 2, 3,
  4, 5, 6,
]

@asterite Sorry. I know you are working for #7443 just now. However I wrote this patch yesterday (but I wrote a spec today.)

[asterite]

@makenowjust Thank you! I didn't start working on this yet, it was just my intention if it was too hard to implement. But you did it so it's great!

[Sija]

You guys are awesome, thanks! 🙇

[kostya]

will this fix #5988?

[asterite]

@kostya I don't think so. However, an idea to fix that is to use the start line and end line of the hash/namedtuple to know what to align. After this is merged I can fix it (or @makenowjust might ^_^)

[sdogruyol]

Thank you @makenowjust 👍