Dependencies: Rework OverlaySheet with the list of dependencies

- Port the whole thing to `pragma ComponentBehavior: Bound`, meaning no
  magical injected contexts are allowed in delegates;
- Create an overlay sheet on demand, reducing startup cost and time;
- Give an overlay sheet focus: there is not much to interact with via
  keyboard, but at least the focus isn't left behind, and it fixes the
  Escape key to close the sheet;
- Set implicit height to the estimated contentHeight, but do it in a
  smart way which doesn't cause back-and-forth loops when the ListView
  changes estimations as user scrolls away from a differently-sized
  section delegate;
- Drop QML import versions, add import aliases;