This PR adds support for plannable import by resource identity, which is first supported in Terraformv1.12.0-beta1.

Today, the only supported plannable import data is theid field, which is just a string that provider typically just redirects to theimport stub state:

import {to=aws_route53_record.myrecordid="Z4KAPRWWNC7JR_dev.example.com_NS"}

Now, if the resource supports identity, the import block will allow the identity to be supplied in theidentity attribute:

import {to=aws_route53_record.myrecordidentity={    zone_id="Z4KAPRWWNC7JR"    record_name="dev.example.com"    record_type="NS"  }}

The identity is automatically passed through to theRead implementation, which typically does the heavy lifting for populating state of an imported resource, however the provider can choose to populate the identity with more information, set data in the import stub state, etc.