Feature Request: Support pretty-printing collection types

[Xulei-NL]

Dear all,

I would like to see terraform fmt support pretty-printing collection types. Currently I observe that internal terraform fmt code runs format passes on fixed lines (please see format.go). But I hope it can help me format variables of collection types (list, set, map), for instance

variable "example_set" {
  type    = set(string)
  default = ["foo", "bar", "dog", "cat", "jojo"]
}

# reformatted to =========================>

variable "example_set" {
  type    = set(string)
  default = [
    "foo", 
    "bar", 
    "dog", 
    "cat", 
    "jojo"
  ]
}

To my understanding, implementing this feature requires replacing the current []formatLine with other data strucutres like linked lists to allow flexible line insertions.

I hope you can put my feature request on your radar! If you don't mind, I'm also willing to implement it if you agree.

Best regards,

Xulei