configs: use addrs.Module for module path, rather than []string

addrs.Module is itself internally just []string, but this better
communicates our intent here and makes this integrate better with other
code which is using this type for this purposes.

configs/config_build.go

@@ -5,6 +5,7 @@ import (
 
 	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/hcl2/hcl"
+	"github.com/hashicorp/terraform/addrs"
 )
 
 // BuildConfig constructs a Config from a root module by loading all of its
@@ -123,7 +124,7 @@ type ModuleRequest struct {
 	// this module. This can be used, for example, to form a lookup key for
 	// each distinct module call in a configuration, allowing for multiple
 	// calls with the same name at different points in the tree.
-	Path []string
+	Path addrs.Module
 
 	// SourceAddr is the source address string provided by the user in
 	// configuration.

configs/configload/module_manifest.go

@@ -5,9 +5,10 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 
 	version "github.com/hashicorp/go-version"
+
+	"github.com/hashicorp/terraform/addrs"
 )
 
 // moduleRecord represents some metadata about an installed module, as part
@@ -43,8 +44,8 @@ type moduleRecord struct {
 // it to reflect any changes to the installed modules.
 type moduleManifest map[string]moduleRecord
 
-func manifestKey(path []string) string {
+func manifestKey(path addrs.Module) string {
-	return strings.Join(path, ".")
+	return path.String()
 }
 
 // manifestSnapshotFile is an internal struct used only to assist in our JSON