Docs examples 04/14: Rework dropdown disclosure examples

Part 4 of 14 in the stack that splits up the approved draft !6295 (closed) into reviewable pieces. The content is exactly what was reviewed there; I've only sliced it.

Related to #3575.

Pages: dropdown disclosure. Also its own MR by size: realistic merge request action menus throughout, examples distributed to their matching Guidelines and Code reference sections, unique titles, and one redundant example removed (it duplicated the page's intro example).

Safe to publish without the MRs after it.