Sensitive area for resizing floating dock widgets is separated from content

Describe the bug
For floating dock widgets, there is some distance between the content and the area that is sensitive for resizing the widget. So to resize a widget, you need to click and drag a bit beyond the border of the widget.

Cause
We give the dock widgets 8px margin deliberately, namely to make space for our custom drop shadow. If we wouldn't do that, the shadow would get clipped.

Unfortunately, the resize-sensitive area does not follow that margin.
Also, the window manager of the OS does not know about that margin, for example on macOS, you can't drag a panel to the very top of the screen: there will always be 8px margin. This might also annoy users.

Proposed solution
For Panels, we could try whether KDDW supports dock widgets with a native window frame, so that the resizing behaviour and drop shadow is generated by the OS. This was also the case in MuseScore 3, and worked well (but yes, that was a totally different docking framework).
For toolbars, a title bar is undesired, so using the native window frame may not be an option there. In that case, we could use the non-native from for those, and disable resizing altogether (which is planned anyway, right?). That would still not solve the problem that you can't drag the window to the top of the screen on macOS though.

Screenshot/video

https://user-images.githubusercontent.com/48658420/145263213-74ed2b4b-bbfa-4f08-90e4-56aca6d7d568.mov

https://github.com/user-attachments/assets/1ccf88d7-1e4d-4a7a-81e8-6da1acbd020f

Keywords for search: undocked panel; hover area

Start by reproducing the resizing and top-of-screen behavior for floating dock widgets, comparing Panels and toolbars. Read the KDDW support for native and non-native window frames, then determine whether the resize-sensitive area can follow the 8px margin without clipping the drop shadow. Done means resizing is reachable from the widget border and the macOS placement issue is addressed or clearly scoped.