Dragging a folder onto a tab should not show drop acceptance feedback

[egamma]

testing #7852

• select a folder in the explorer
• drag it onto a tab

-> the tab shows acceptance feedback, but when dropping the folder nothing happens, except some temporary flickering.

I would have expect that no drop acceptance feedback is shown.

[bpasero]

@egamma unfortunately all I have is a resource URI and from that I do not know if it is a folder or not. Same is true when dragging from the desktop.

[bpasero]

Some things:

• dragging from the desktop ideally contains information about the resource being dragged being a folder or not
• dragging a file from the tree should use the same native file transfer

I think there is some upstream dependencies on this issue.

[bpasero]

i pushed a fix so that this no longer happens for dragging from outside Code into Code because it was needed for #8726