generate: Prevent automatic id attribute behaviors under blocks

[bflad]

Closes #335

Previously, the automatic id attribute handling intended for root level schema blocks was applied to all blocks, causing the generator to errantly set the grouping to Read-Only and the description to The ID of this resource. This was captured via a new integration test:

--- FAIL: Test_SchemaJson_GenerateAcceptanceTests (0.00s)
    --- FAIL: Test_SchemaJson_GenerateAcceptanceTests/nested_id_attribute (0.25s)
        testscript.go:558: # Copyright (c) HashiCorp, Inc.
            # SPDX-License-Identifier: MPL-2.0
            # Ensure only root level id attribute receives automatic description (0.236s)
            > [!unix] skip
            > exec tfplugindocs --provider-name=terraform-provider-scaffolding --providers-schema=schema.json
            [stdout]
            rendering website for provider "terraform-provider-scaffolding" (as "terraform-provider-scaffolding")
            exporting schema from JSON file
            getting provider schema
            generating missing templates
            generating missing resource content
            generating new template for "scaffolding_example"
            generating missing data source content
            generating missing function content
            generating missing provider content
            generating new template for "terraform-provider-scaffolding"
            rendering static website
            cleaning rendered website dir
            rendering templated website to static markdown
            rendering "index.md.tmpl"
            rendering "resources/example.md.tmpl"
            > cmp stdout expected-output.txt
            > cmp docs/index.md expected-index.md
            > cmp docs/resources/example.md expected-resource.md
            diff docs/resources/example.md expected-resource.md
            --- docs/resources/example.md
            +++ expected-resource.md
            @@ -48,17 +48,17 @@
             <a id="nestedblock--list_nested_block_optional_id"></a>
             ### Nested Schema for `list_nested_block_optional_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Optional:
            +
            +- `id` (String)

             <a id="nestedblock--list_nested_block_required_id"></a>
             ### Nested Schema for `list_nested_block_required_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Required:
            +
            +- `id` (String)

             <a id="nestedatt--optional_object_attribute"></a>
            @@ -72,33 +72,33 @@
             <a id="nestedblock--set_nested_block_optional_id"></a>
             ### Nested Schema for `set_nested_block_optional_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Optional:
            +
            +- `id` (String)

             <a id="nestedblock--set_nested_block_required_id"></a>
             ### Nested Schema for `set_nested_block_required_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Required:
            +
            +- `id` (String)

             <a id="nestedblock--single_nested_block_optional_id"></a>
             ### Nested Schema for `single_nested_block_optional_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Optional:
            +
            +- `id` (String)

             <a id="nestedblock--single_nested_block_required_id"></a>
             ### Nested Schema for `single_nested_block_required_id`

            -Read-Only:
            -
            -- `id` (String) The ID of this resource.
            +Required:
            +
            +- `id` (String)

             <a id="nestedatt--computed_object_attribute"></a>
            @@ -114,7 +114,7 @@

             Read-Only:

            -- `id` (String) The ID of this resource.
            +- `id` (String)

             <a id="nestedblock--set_nested_block_computed_id"></a>
            @@ -122,7 +122,7 @@

             Read-Only:

            -- `id` (String) The ID of this resource.
            +- `id` (String)

             <a id="nestedblock--single_nested_block_computed_id"></a>
            @@ -130,4 +130,4 @@

             Read-Only:

            -- `id` (String) The ID of this resource.
            +- `id` (String)

            FAIL: testdata/scripts/schema-json/generate/nested_id_attribute.txtar:9: docs/resources/example.md and expected-resource.md differ

The schema rendering logic could likely use a full refactoring as it has very high code complexity, but this change is only a very targeted fix for the acute and errant id attribute handling behavior.

[austinvalle]

LGTM 🚀

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