Work items back button navigation from non-page contexts

Originally discussed in !91469 (comment 1023398196)

Summary

When opening work items in modal or drawer contexts, the browser back button should act as though the modal/drawer is a page and return the user to the last context. In other words, if a user opens a task from an issue in a modal, back should return me to the issue by closing the modal.

This will be more important in later iterations as users have more tools to traverse lists and move from work item to work item. This behavior should be consistent regardless of the container in which the work item is displayed.