Filter out headings from tables and lists when building Table of Contents

[stevencohn]

Currently, headings that are embedded in tables and lists are included in the table of contents.

Add an option to the TOC dialog to include these explicitly and exclude them by default.

Note: this may be viewed as a breaking change to some users.
Note: secondary headings are included in the Navigator window; should they be?

[github-actions]

Merged in PR #2193: 2192-secondary-headings-in-toc

[github-actions]

Merged in PR #2195: 2192 secondary headings outlined

[jasonjac2]

Interesting - for me a heading is a heading is a heading :-). I rely on them in ToC and would hope to keep them in Navigator. But I can see that people organise their pages in such a way as not to want them.