We have new Symfony-based routes, and Views UI has a lot of routes.
Some of them, it turns out, are redundant.
The first step will be to just convert them, with as little changes as possible. This means loading views_ui/admin.inc in several methods, and decoupling later.
It also exposes some wonkiness in the routing system, which I will open a meta for soon, and link here.
#1889790: [Meta] Allow modules to register links for menus, breadcrumbs and tabs (if not with hook_menu) already outlines some of the problems, but hook_menu() still works for breadcrumbs, local actions, and local tasks (even default). However, contextual links do not seem to work at all.