didyoumean: move from "helper" to "internal"

This new-ish package ended up under "helper" during the 0.12 cycle for
want of some other place to put it, but in retrospect that was an odd
choice because the "helper/" tree is otherwise a bunch of legacy code from
when the SDK lived in this repository.

Here we move it over into the "internal" directory just to distance it
from the guidance of not using "helper/" packages in new projects;
didyoumean is a package we actively use as part of error message hints.

configs/configschema/validate_traversal.go

@@ -8,7 +8,7 @@ import (
 	"github.com/hashicorp/hcl/v2/hclsyntax"
 	"github.com/zclconf/go-cty/cty"
 
-	"github.com/hashicorp/terraform/helper/didyoumean"
+	"github.com/hashicorp/terraform/internal/didyoumean"
 	"github.com/hashicorp/terraform/tfdiags"
 )
 

terraform/evaluate_valid.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs"
-	"github.com/hashicorp/terraform/helper/didyoumean"
+	"github.com/hashicorp/terraform/internal/didyoumean"
 	"github.com/hashicorp/terraform/tfdiags"
 )