configs: check for errors after LoadHCLFile

[mildwonkey]

The configs package was not checking the diagnostics for errors after loading files as HCL, which lead to panics in init and validate when terraform encountered invalid HCL.

The following config would produce an error out of terraform fmt, which explicitly validates the syntax first, but cause a panic in init or validate:

provider "aws" {
  region = var.aws_region
  version =
}

I think a follow-up HCL issue to improve the output in this instance is warranted:

$ terraform validate

Error: Invalid expression

  on main.tf line 3, in provider "aws":
   3:
   4:

Expected the start of an expression, but found an invalid expression token.

Fixes #21518

[mildwonkey]

solution v2! Gracefully handle unexpected cty.DynamicVals in the version attribute.

[mildwonkey]

I did spend some time playing with go-fuzz, and I'll save that work in a branch for now but I have yet to coerce any new panics out of it.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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