Ability to skip some headings in the TOC

One idea would be to use a rendering parameter on HeadingBlock to tell the TOC macro to not include this heading. See also NBREF-12 which introduced the data-xwiki-rendering-protected parameter to tell the Numbered Reference Extension to skip numbering a heading.

Either reuse this same parameter name or introduce a new one (and probably refactoring data-xwiki-rendering-protected too since it feels too generic). It seems the 2 use cases are different (both about rendering):

• skipping numbering
• skipping being in the TOC

If we have only one then it means we couldn't skip numbering and still keep the heading in the TOC at the same time. That feels like a valid use case to me. WDYT?