Add a text filter to generate the Table of Contents in the text

Problem/Motivation

toc_js currently exposes its TOC via a block. This works well for Layout Builder pages or theme-level placements (e.g., in a node Twig), but it does not give editors per-content, in-body control of where the TOC appears. They cannot place the TOC after an intro paragraph, between sections, etc.

This change adds a Text Filter that lets authors insert a simple token ([toc]) at the desired location in the body. The filter reuses the existing toc_js block (and its configuration/options) and renders that block output exactly where the token appears—delivering the same frontend behavior with much finer editorial control.

Steps to reproduce

1. Enable toc_js and add its TOC via the provided block.
2. Create a node with multiple headings (h2/h3).
3. Attempt to place the TOC inside the body (e.g., after the first paragraph) without Layout Builder or theme overrides.
4. Observe: it’s not possible—only block placement is available; token-based placement is missing.

Proposed resolution

Add a CKEditor 5-compatible Text Filter that:

• Exposes the same configuration options as the existing toc_js block (heading levels/depth, label, container classes, etc.) on a per-Text-Format basis.
• Programmatically renders the existing toc_js block at the token location, so output and behavior match the block 1:1.
• Attaches the toc_js library exactly once; guards against duplicate attachments.
• Ensures correct cacheability (contexts/tags/max-age) propagate from the block to the filter result.

User interface changes

• New filter “Toc.js shortcode: [toc]” (provided by the toc_js_filter submodule) appears under Configuration → Content authoring → Text formats and editors.
• Filter settings fieldset per Text Format mirrors the toc_js block options (heading levels, depth, label, classes, list type, numbering, anchor prefix, scope selector).
• No new standalone admin pages.

API changes

• None. Adds a new Text Filter in a submodule that reuses the existing toc_js block plugin; no public API changes in toc_js itself.

Data model changes

• No new entities/tables.
• New config schema for the filter’s per-Text-Format settings stored with Text Format config; keys mirror the block’s options.