Do not sanitize asciidoc toc class

What does this MR do and why?

Allow the AsciiDoc table of contents class to not be sanitized, and add simple bold styling to the title.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to the wiki

2. Create a new page in Asciidoc format

3. Paste the following

   = Asciidoc Test
   :toc:
    
   == Level 2
    
   === Level 3
    
   == Level 2

MR acceptance checklist

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Related to #246501 (closed)