Backport of fix: don't reveal nested attributes with sensitive schema into v1.3

[ghost]

Backport

This PR is auto-generated from #32004 to be assessed for backporting due to the inclusion of the label 1.3-backport.

The below text is copied from the body of the original PR.

---

Description

Fixes several bugs in the plan diff rendering of nested attributes

• When a schema attribute is sensitive, but also contains nested attributes, terraform reveals the nested attributes. The renderer checks for sensitive values at this nesting level, but ignores sensitive schema.
• There is a mixture of "(sensitive)" and "(sensitive value)" output in the plan diff and I changed them all to "(sensitive value)"
• Certain nested attribute modes don't output consistent new values for delete plans or unknown values

I also added a lot more test coverage for single nested attribute mode and sensitive schema nested attributes

Sample Config

terraform {
  required_providers {
    nested = {
      source = "alisdair/nested"
    }
  }
}

resource "nested_single" "example" {
  name = "my_nested_single"

  sensitive_value = {
    string = "secret"
  }
}

resource "nested_list" "example" {
  name = "my_nested_list"

  sensitive_values = [{
    string = "secret"
  }]
}

resource "nested_blocks" "example" {
  name = "my_nested_list"

  list {
    sensitive_value = {
      string = "secret"
    }
  }
}

Before:

After:

Target Release

1.4.0, 1.3.5

Draft CHANGELOG entry

BUG FIXES

When rendering a diff of nested attributes, Terraform now hides the entire nested object if it is marked sensitive by the provider schema

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