For Katerina: beginnings of drag/drop accessibility enhancements

[nicolethoen]

My approach/plan:

• If the Draggable item has no interact-able elements within it, then it does not need a drag button because we can put a tab index on the Draggable item to allow the user to put focus on the item. If it does have interact-able elements within it - such as a button or dropdown or link - then the tab index would go on a DragButton component, which is basically just a button with the drag icon that will consume a context passed down from the Draggable item. The consumer would need to manually add the DragButton to each Draggable item in that case.
• In order to take advantage of all the logic associated with animating everything correctly and applying the correct styles at the right times, I tried to invoke the mouse events from within the keyboard events. I'm only midway through that attempt so it's definitely very messy.
• The current Draggable component (before I started messing with it) used a lot of instance variables rather than state management to pass crucial information between the various even handlers. That is currently one of the most difficult things to incorporate into the keyboard handling. I've tried to refactor it so that event handlers are passing crucial information around via function parameters instead - but now everything feels very tangled and I need to sort it out.
• so far, you can use the keyboard to begin dragging an item (without a drag button), but I have not figured out how to drop that item correctly yet, and I have not yet tried to figure out how to move the dragging item very far. There's a lot let to work on

I have no begun to think about screen reader usage. I think that may need to be a follow up issue. The largest hurdle I see there is that screen readers rely heavily on click events, and our drag/drop component uses mouseup/mousedown events so it may not translate naturally based on our current approach.

[patternfly-build]

Preview: https://patternfly-react-pr-6626.surge.sh

[stale]

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