Define how to handle secondary local tasks in entity pages when Navigation Top Bar is enabled

We've added this to the admin UI design backlog, but with lower priority since it isn't a Navigation Stable blocker and no core modules need 2nd level items. The first idea was implementing a drop-down, but we are not sure if that's really the best UI pattern based on the problems it should solve. Also in the future we’ll need to evaluate if we want to keep dividing the drop down from the right sidebar on entities as two different things, and if so define clear rules.

Changing the priority to Minor for now.

Made a couple of simple proposals to try to unblock this one:

When there are 2 level tasks, show the 1st level in the page actions drop down and shown the 2nd level tasks as 2nd level tasks, like in the original behavior:

When there are 2 level tasks, show the 1st level in the page actions drop down and shown the 2nd level tasks as 1st level tasks, promoting them one level:

Any of these options would not need to define any extra design, nor define complex behaviors. They just set a rule about how to deal with the 2nd level local tasks in a generic way.

We just discussed it with @plopesc and this still needs some definition in terms of UX for the different situations this would end ups giving a solution to, so it needs to be addressed more holistically and taking into account the changes XB is bringing into the future of the UI. So postponing this as "Needs design" since we'll work on defining it first.

While this is still in the design phase, I'd like to point to an issue from the Trash module, which uses 2nd level tasks for each trash-enabled entity type. The problem raised there shows that there could be as many as 15-20 2nd level tasks, and it probably won't work very well with the proposal from #4.