Let edit icons not all show persistently in preview (show all once and then individually as needed)

I think it is great that the edit icons show what elements in the preview can be edited, in a way that is much better than “shift click to edit” tooltip. However, they also seem to be somewhat distracting and get in the way of preview. Could the icons all appear momentarily when the preview first loads or when first hovering over the preview and then fade away? Could individual icons then re-appear when hovering over (or focusing on) the element associated with a given icon?

Start by locating the preview edit-icon rendering and the handlers for preview hover, element hover, and focus. The change is done when all icons briefly appear on initial preview interaction, fade away, and individual icons reappear for their associated elements on hover or focus.

Written by the indexing model from the issue text.