[UX] Show parent information in work items views

Problem to solve

When working in different planning views, it is important to understand if an item belongs to a larger effort (parent) and be able to identify that information without needing to open or navigate to the item.

Proposal

Display a new Parent field on items within planning views which identifies the direct parent (if it exists) along with the ability to see more details regarding the parent item upon hover using a Popover component (following similar pattern to our item reference popovers like seen in descriptions/comments/activity area).

• Add the Parent field to items in the following areas:
  • List view
    • Ensure Parent is added to the display options on the List page, so it can be hidden if desired
  • Linked items & Child items widgets
    • If #393558 (closed) is completed prior to this, it would be ideal to have the Parent display option off by default for the Child items widget since that information is fairly apparent in that context. This keeps the widgets consistent though in what they offer for display options, and for cases where users find value (ex: multi-level nesting) it can be beneficial to still offer the ability to see the Parent within items from the Child items widget.
  • Board view (this will be handled on the new boards experience)
  • Table view (will be included in &9571)
• Use the work-item-parent icon along with the Title when displaying the field
  • Truncate the Title so it has a max-width of 9rem (144px)
  • On hover/focus of the Parent field, display the reference popover we use for items, along with a header that reads "Parent" (see design).