tests/provider: Enable tfproviderlint R004 check (#11499)

* tests/provider: Enable tfproviderlint R004 check

Reference: https://github.com/bflad/tfproviderlint/blob/master/passes/R004/README.md
Reference: #9954

* resource/aws_s3_bucket: Fix complex import of aws_s3_bucket_policy to properly set policy in state

Found via linting:

```
/Users/bflad/src/github.com/terraform-providers/terraform-provider-aws/aws/import_aws_s3_bucket.go:36:22: R004: ResourceData.Set() incompatible value type: *github.com/aws/aws-sdk-go/service/s3.GetBucketPolicyOutput
35		pData.Set("bucket", d.Id())
36		pData.Set("policy", pol)
37		results = append(results, pData)
```

This type of complex import (importing multiple resources) is likely to be removed in a future major version.

Output from relevant acceptance testing (other tests do not perform necessary ImportStateCheck to verify complex import):

```
--- PASS: TestAccAWSS3Bucket_Policy (95.74s)
```

GNUmakefile

@@ -64,6 +64,7 @@ lint:
 		-AT002 \
 		-AT006 \
 		-AT007 \
+		-R004 \
 		-S001 \
 		-S002 \
 		-S003 \

aws/import_aws_s3_bucket.go

@@ -33,7 +33,7 @@ func resourceAwsS3BucketImportState(
 	pData.SetId(d.Id())
 	pData.SetType("aws_s3_bucket_policy")
 	pData.Set("bucket", d.Id())
-	pData.Set("policy", pol)
+	pData.Set("policy", pol.Policy)
 	results = append(results, pData)
 
 	return results, nil