Ability to see the breakdown of an epic in their tasks (with a + collapsible)

When using Roadmaps in both Next-Gen and Classic Projects:

I want to see a breakdown of the user stories in which an epic splits in the Roadmap view

So that I am able to see how the work on the epic goes and what is development pending ...

Acceptance Criteria

1. In the roadmap view, there will be an arrow to view or collapse all the US/Tasks from an epic.
2. In the roadmap view, each US/Task should have its own dates (start date and due date) reflected in the roadmap (as a "Gantt project" would show)
3. The user can drag the US/Task to a different order
4. The US/Task should be ordered by start date as default order.
5. A user can select a US/Task to edit or delete it