importstate: Use ExpectNonEmptyPlan field to ignore no-op assertion for import block test kinds

[austinvalle]

Related Issue

N/A

Description

This change adds the usage of (TestStep).ExpectNonEmptyPlan to ignore the assertion that all import block plans must produce a no-op. A no-op plan isn't possible for some resource types that cannot return the entire original value from the remote API after importing. The usage of ImportPlanChecks can be used to make more fine-grain assertions about the plan to ensure the plan produced during import is correct.

Test failure prior to introducing the change:

--- FAIL: TestImportBlock_WithID_ExpectNonEmptyPlan (0.75s)
    /Users/austin.valle/code/terraform-plugin-testing/helper/resource/importstate/import_block_with_id_test.go:105: Step 2/2 error running import: importing resource examplecloud_container.test: expected a no-op import operation, got ["update"] action with plan 
        stdout:
        
        
        Terraform used the selected providers to generate the following execution
        plan. Resource actions are indicated with the following symbols:
          ~ update in-place
        
        Terraform will perform the following actions:
        
          # examplecloud_container.test will be updated in-place
          # (imported from "westeurope/somevalue")
          ~ resource "examplecloud_container" "test" {
              ~ id       = "westeurope/somevalue" -> (known after apply)
              ~ location = "westeurope" -> "eastus"
                name     = "somevalue"
            }
        
        Plan: 1 to import, 0 to add, 1 to change, 0 to destroy.
FAIL
FAIL	github.com/hashicorp/terraform-plugin-testing/helper/resource/importstate	1.407s
FAIL

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Nope.

[rainkwan]

Looks reasonable, we can revisit the flagging question later if needed.

[SBGoods]

I'm also fine with reusing ExpectNonEmptyPlan since it's behavior is already well understood.