core: Update test fixtures for ProviderTransformer tests

Some of these tests were using an outdated form to reference a local
directory as a module. While here, I also updated the provider references
to the new unquoted form, which is preferred from v0.12 onwards.

terraform/test-fixtures/transform-provider-grandchild-inherit/child/main.tf

@@ -5,6 +5,6 @@ provider "aws" {
 module "grandchild" {
   source = "./grandchild"
   providers = {
-    "aws.baz" = "aws.bar"
+    aws.baz = aws.bar
   }
 }

terraform/test-fixtures/transform-provider-grandchild-inherit/main.tf

@@ -4,8 +4,8 @@ provider "aws" {
 }
 
 module "child" {
-  source = "child"
+  source = "./child"
   providers = {
-    "aws.bar" = "aws.foo"
+    aws.bar = aws.foo
   }
 }

terraform/test-fixtures/transform-provider-implicit-module/main.tf

@@ -5,6 +5,6 @@ provider "aws" {
 module "mod" {
   source = "./mod"
   providers = {
-    "aws" = "aws.foo"
+    aws = aws.foo
   }
 }

terraform/test-fixtures/transform-provider-inherit/child/main.tf

@@ -3,5 +3,5 @@ provider "aws" {
 }
 
 resource "aws_instance" "thing" {
-    provider = "aws.bar"
+    provider = aws.bar
 }

terraform/test-fixtures/transform-provider-inherit/main.tf

@@ -4,8 +4,8 @@ provider "aws" {
 }
 
 module "child" {
-  source = "child"
+  source = "./child"
   providers = {
-    "aws.bar" = "aws.foo"
+    aws.bar = aws.foo
   }
 }

terraform/test-fixtures/transform-provider-invalid/main.tf

@@ -6,6 +6,6 @@ module "mod" {
   
   # aws.foo doesn't exist, and should report an error
   providers = {
-    "aws" = "aws.foo"
+    aws = aws.foo
   }
 }