Replace usage of DescriptionList where not semantically correct

[imiric]

Currently we use our custom DescriptionList element in a few places:

• For the glossary.

• For the "Private load zones" FAQ

• For the "Test status codes" list.

• For the "Where to set options" section on the "How to use options" page.

• Since large tests, edit structure, format, and sentences #1003, on the new "Running large tests" page, currently also being updated in Update "Running large tests" article #992.

As explained in this comment, this element is not appropriate to use simply because of its indented style. It makes semantic sense for the first 3 examples, since they are term definitions or short lists without much text, but not for the last 2, since these are not definitions or descriptions, but are used only because of the styling. If we need a similar style, we should create another custom element that wraps a title in a header element, and indent normal paragraphs following it with a bit of CSS.

This would generate much simpler semantic markup, wouldn't require fixes for issues like #1002, and would avoid the risk of any accessibility quirks.