Config-driven importing through identity (TF-23179)

[dbanck]

This PR adds support for importing resources via their identity

Target Release

1.12.x

CHANGELOG entry

I'm planning to add changelog entries for the whole feature in a separate PR

[austinvalle]

Apologies for creeping on this PR 👀 , but I was just perusing how close this PR is to ready. I found one (already in main) decode problem here -> #36806 .

The other problem I ran into was something this PR may eventually have resolved so I'm just dropping it here 😄.

Currently, when importing by identity, the actual identity data isn't passed to the following ReadResource RPC call since it's not being added to the ResourceInstanceObject:

• terraform/internal/terraform/node_resource_plan_instance.go

  Line 766 in 7e069d4

  importedState := states.NewResourceInstanceObjectFromIR(imported[0])

• terraform/internal/states/instance_object.go

  Lines 70 to 76 in dcb06b9

  	func NewResourceInstanceObjectFromIR(ir providers.ImportedResource) *ResourceInstanceObject {
  	return &ResourceInstanceObject{
  	Status: ObjectReady,
  	Value: ir.State,
  	Private: ir.Private,
  	}
  	}

---

With both of those resolved, looks like the data is properly passed around after that with some basic smoke tests 🎉

[jbardin]

LGTM! We can probably get rid of those getProvider calls since you're not using the provider. That little wrapper is a bit weird, and a result of refactoring long ago, but I'm not sure what to do with it for now since it does cut down on some repetition when providers are used.