Port of ArtPreviewOverlay.slint: hovering the small cover floats a 220px
preview above it. Missing in every bar mode except Large.
Non-interactive and mounted last in AppShell, both for the reason the
.slint records: the original used a PopupWindow and it stole the hover
from the trigger, so the preview flickered open and shut. An overlay that
cannot receive events cannot do that, and clicks pass through.
The anchor rides QbzShell like the drag ghost does -- trigger and overlay
are in different files with no shared id.
cc
vicrodh
8b26cda6f6