Animate launching apps from event coords

## Problem

Interacting with items in apps that open via another app usually results in the new window with said contents appearing out of nowhere.

## Proposal

There is some way for a custom listview widget to tell Gala its X+Y coordinates relative to the app window so that Gala can:
- Add them to the X+Y of the window relative to the aspect ratio and;
- Animate the app 'expanding out of the item' in a similar fashion to how gala does fullscreen/unfullscreen animations.

## Prior Art

MacOS does this when you 'get info' on an item, and I think when you open images from Finder in newer versions of macOS