Issue #2406749 by dawehner, YesCT, amateescu, hussainweb, kim.pepper, RavindraSingh, pwolanin, Wim Leers, Gábor Hojtsy, yched, jibran: Use a link field for custom menu link

Issue #2282519 by alexpott, cilefen: Fixed Add content dependency information to configuration entities.

Issue #1777332 by hass, Cottser, mike.roberts, joelpittet, dawehner | jenlampton: Replace theme_menu_link() and menu-tree.html.twig with a single Twig template.

Issue #474004 by mdrummond, kim.pepper, Wim Leers, jibran, tim.plunkett, joachim | JohnAlbin: Add options to system menu block so primary and secondary menus can be blocks rather than variables.

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).