Ctrl+T doesn't select the bounds of the attachment (selects the whole tile, even empty pixels)

Ctrl+T should select the bounds of the content, useful to see the transformation handles for the attachment then.

Some other commands that should show only the bounds (or take care only of the attachment bounds):

* Move tool (Ctrl key)
* Shift+H and Shift+V to flip the attachment (about this one we talked that a new attachment could be created, probably the best way would be that Shift+H or Shift+V just modify the current attachment, so if a new attachment is required, it can be duplicated before)

Start by reproducing Ctrl+T on an attachment with transparent or empty pixels and inspect the attachment-bounds handling. Then check the Move tool's Ctrl behavior and Shift+H/Shift+V; done means these operations use the attachment bounds rather than the whole tile, with the flip behavior clarified for existing versus duplicated attachments.

Written by the indexing model from the issue text.