Follow up to#468

Some initial feedback rightfully pointed out that it's likely that providers will want to assert the entire identity object as a single check, rather than multiplestatecheck.ExpectIdentityValue checks. We can have both, so this PR introduces the object-level check (similar toknownvalue.ObjectExact).

This PR also uses theValueType method that was recently updated interraform-plugin-go@main ->hashicorp/terraform-plugin-go#497