qml: player toolbar editor dialog improvements

Consists of mostly non-visual changes for the qml toolbar editor. Also fixes #25644 (closed).

60f66682 uses an unorthodox way (width/height set to 0 instead of visible set to false) to achieve its purpose (dragging a control over tab button to change the selected player toolbar). I found some alternatives, but they introduced other issues because of the ListView, so I went with it. The problem is, Qt does not like it when a dragged item's source becomes invisible during dragging. I can remove that specific patch if the feature is not needed.