Should rectangular bounds of selection

## Requested feature

Please show the rectangular selection (and maybe top-left-corner) in pixel-sizes, e.g. in the status bar.

### Possible drawbacks

I'm not aware of any.

### Possible alternatives

None.

## Use case

I often need to measure sizes of GUI controls in screenshots and don't want to transfer the file first to Windows to do it there with Paint.net.

Start by locating the selection UI and status-bar entry points in the Python application, then run the app and create a rectangular selection. Done means the selection's pixel width and height are shown, with the top-left position included only if the existing UI supports it.

Written by the indexing model from the issue text.