Fix Wayland : Preserve Drag Preview For Non-Floatable Dock Widgets

[Deception666]

* Fix Wayland Non-Floatable Dock Widget

  - Prevent Wayland drag previews from being cancelled when a non-floatable dock
     widget leaves its source window
  - Keep the preview frozen until the cursor re-enters the source window or the
    drag is cancelled
  - Pass dock widget floatable state through title bar and tab drag handling
  - Add CDockWidgetTab::isFloatable() helper
  - Update waylandMoveOrLeaveInWindowPreview() documentation and behavior

* Repurpose ConfigFlags Example : Expand Example to Configure Dock Manager And Widget Flags
    
  - Add UI for interactively selecting DockManager and AutoHide configuration flags
  - Add dynamic creation of dock widgets with configurable DockWidget features
  - Support Calendar, Dial, LCD Number, and Text Edit example widgets
  - Add custom close handling demonstration
  - Refactor MainWindow initialization to accept an externally configured DockManager
  - Add Qt 5 high-DPI configuration for the example

Wayland Before and After

wayland-before.webm

wayland-after.webm

Windows Before and After

windows-before.webm

windows-after.webm

X11 Before and After

x11-before.webm

x11-after.webm