Add resource identity to Move RPC

[rainkwan]

Follow-Up PR for #1112

This PR implements MoveResourceState (Move) for identity.

[austinvalle]

Overall everything is looking good! I had a couple questions/nits

[austinvalle]

This is the scenario we're trying to prevent, if a provider does this it'll send back identity data to Terraform despite it not "announcing" an identity schema for the resource 🙂:

Suggested change

	// Try to set TargetIdentity even though req.IdentitySchema is nil
	resp.Diagnostics.Append(resp.TargetIdentity.SetAttribute(ctx, path.Root("test_id"), "should-not-be-set")...)
	// This resource doesn't indicate identity support (via a schema), so this should raise a diagnostic.
	resp.TargetIdentity = &tfsdk.ResourceIdentity{
	Raw: tftypes.NewValue(testIdentitySchema.Type().TerraformType(ctx), map[string]tftypes.Value{
	"test_id": tftypes.NewValue(tftypes.String, "should-not-be-set"),
	}),
	Schema: testIdentitySchema,
	}

[rainkwan]

This doesn't raise a diagnostic now, should it?

https://github.com/hashicorp/terraform-plugin-framework/pull/1123/files#diff-599c61942d4492eedc1e197f8fd0cb49150b360ca7fc4b6939815ab637cc6eb8R930-R980

[austinvalle]

Yeah it should be raising a diagnostic, it looks like the check being on line 228 was too early because resp.TargetIdentity is not set at that point (it's at moveStateResp.TargetIdentity when it comes back from your provider code that sets it).

Other RPCs just immediately set resp.Identity after the RPC, but if you want to move that piece of logic down lower we can also do that!

I'll make a comment suggestion 👍🏻

[austinvalle]

🎉