Use Window instead of Control for grab preview

[DS204ever]

Changed drag preview from control to window which fixes viewport clipping issues.

Changelog:

• Changed drag preview type from Control to Window.
• Added new method in Window which changes window's position to mouse's in order to track mouse position.

Relations:

• fix Drag previews clipped by Popup that created them #67186
• alternative to Allow drag_preview to be handled by a different viewport than its parent #64949
• related to Enable Drag and Drop between SubViewports and Windows #67531

Known issues:

• When the global project setting embedded subwindows is enabled it is not possible to drag and drop data from the main window into an external window.

embedded_windows.mp4

external_windows.mp4

[DS204ever]

Unit tests were failing in test case [TextEdit] text drag.
I think that the mouse event wasn't updating the window drag preview correctly or enough times for it to change location, I increased the movement amount before releasing the drag in an attempt to fix this and it seems to have worked.
I have also replicated the test manually in the editor and it behaves as expected, which leads me to believe this is only an issue for the unit test and does not replicate the real scenario.