Animate in + down panel item popovers

### Problem

In OS 9, we lose the "arrow" indicator at the Popover edge, linking the content to the item. In #704, we added the :checked state to panel items to instead make panel items remain visually connected to the popover that it opens. I thought another way (as mentioned in #703) to improve this paradigm would be to animate-in + down the popover from the wingpanel (assuming it's always at the top of the screen) for better feel.

### Proposal

Animate in + down a wingpanel popover when it opens.

### Prior Art (Optional)

_No response_