src/vs/workbench/browser/parts/editor/editorDropTarget.ts/DropOverlay/isCopyOperation
class DropOverlay:	private isCopyOperation(e: DragEvent, draggedEditor?: IEditorIdentifier): boolean {
		if (draggedEditor?.editor.hasCapability(EditorInputCapabilities.Singleton)) {
			return false;
		}

		return (e.ctrlKey && !isMacintosh) || (e.altKey && isMacintosh);
	}