Issue #1805054 by Wim Leers, Gábor Hojtsy, effulgentsia, jibran, jessebeach, catch, dawehner, Fabianx, sun, larowlan: Cache localized, access filtered, URL resolved, and rendered menu trees

Issue #2479363 by Wim Leers, dawehner: Cache MenuActiveTrail::getActiveIds() for *all* menus per route match: 1 cache get instead of N DB queries, saves 1 ms/response

Issue #2422363 by mortendk, joelpittet, davidhernandez: Rewrite the menu CSS components inline with our CSS standards

Issue #2425691 by pjbaert, kepford, drupalninja99: Remove .leaf/.menu-item--leaf from menu CSS components

Issue #2040135 by Wim Leers, Berdir: Caches dependent on simple config are only invalidated on form submissions

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 #2340123 by Wim Leers: Setting cache tags can be tricky: use strings instead of nested arrays to improve DX.

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 #2305707 by cilefen, pwolanin, dawehner, LinL: MenuLinkContent disabled field should be renamed to enabled and use positive logic.

Issue #2301317 by pwolanin, dawehner, Wim Leers, effulgentsia, YesCT, xjm, alexpott: MenuLinkNG part4: Conversion.

Revert "Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion."

This reverts commit fd2db9cd.

Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion.

Issue #2301273 by pwolanin, dawehner, Wim Leers, effulgentsia, joelpittet, larowlan, YesCT, kgoel: MenuLinkNG part2 (no UI or conversions): MenuLinkTree API and unit tests.