Use upstreamed HCL typexpr package

[jpogran]

Replace internal copy of typeexpr package from Terraform core with the typeexpr package that was upstreamed back to HCL v2.14.0.

Currently we use a copy of typeexpr package from Terraform Core which represents Terraform 0.14 - 1.2.

The v1.2 functionality was upstreamed back to HCL v2.14.0 and Terraform Core switched back to that upstream and removed its own copy of the typeexpr package in hashicorp/terraform#31729

Part of hashicorp/terraform-ls#917

[radeksimko]

LGTM!

Just to clarify, for posterity - the expectation is that this change is no-op for the end-user, right?

Given that despite using the newer upstream implementation, the TypeConstraint method we use still represents the old <1.3 style type declaration which will continue to error on the defaults, such as in this snippet:

variable "test" {
  type = object({
    foo = string
    bar = optional(string, "toot")
  })
}

I am guessing the next step, which can be a separate PR, would be to leverage the new method TypeConstraintWithDefaults and fall back to TypeConstraint, which I think is what Terraform internally probably does. At least that's how the documentation suggests it works.

https://pkg.go.dev/github.com/hashicorp/hcl/[email protected]/ext/typeexpr#TypeConstraintWithDefaults

TypeConstraintWithDefaults attempts to parse the given expression as a type constraint which may include default values for object attributes. If successful both the resulting type and corresponding defaults are returned. If unsuccessful, error diagnostics are returned.