[ToolTipManager] Create DolphinFileMetaDataWidget on-demand again
This reverts b7fbd19a but creates the widget only once and then reuses it. However, ownership of a parent-less widget is transferred to the `KToolTipWidget` but since we first request metadata, then show the tooltip (or won't if the mouse moved on since), we cannot rely on the `KToolTipWidget` exclusively. Instead, when we still delete the widget ourself until we have shown the `KToolTipWidget` once at which point it will handle the life time for us. This fixes parenting the widget to `DolphinView` which would make it appear as a broken line in the top left of the window.