Support refactoring "Extract variable"

In Intellij, for languages like Java, you have refactoring support. This might become very handy in the HCL plugin too to support Terraform refactorings.

The first refactoring I would like to see supported is to replace a constant value with a variable, given the constant value as a default value.

On top of that, the existence of a file variables.tf seems to be best practice although it is not necessarily needed. But if we follow best practices, the refactoring “Extract variable” should put the variable in the variables.tf file and create this file when it doesn’t exist yet.

[VladRassokhin]

Here’s test version of plugin if you’d like to try new refactoring.

[mkuzmin]

before:

resource "tls_private_key" "ssh" {
  algorithm = "RSA"
}

after:

variable "algorithm" {
  default = "RSA"
}
resource "tls_private_key" "ssh" {
  algorithm = "${var.algorithm}"
}