fixed drag and drop issues from files into folders in solution explorer (#4095)

vsintegration/src/FSharp.ProjectSystem.Base/Project/ProjectNode.CopyPaste.cs

@@ -39,11 +39,6 @@ public override int DragEnter(IOleDataObject pDataObject, uint grfKeyState, uint
         {            
             pdwEffect = (uint)DropEffect.None;
 
-            if (this.SourceDraggedOrCutOrCopied)
-            {
-                return VSConstants.S_OK;
-            }
-
             this.dropDataType = QueryDropDataType(pDataObject);
             if (this.dropDataType != DropDataType.None)
             {

vsintegration/src/FSharp.ProjectSystem.Base/Project/ProjectNode.cs

@@ -4922,8 +4922,12 @@ internal int AddItemWithSpecific(uint itemIdLoc, VSADDITEMOPERATION op, string i
                             
                             if (context == AddItemContext.Paste && FindChild(file) != null)
                             {
-                                // if we are doing 'Paste' and source file belongs to current project - generate fresh unique name
-                                newFileName = GenerateCopyOfFileName(baseDir, fileName);
+                                newFileName = Path.Combine(baseDir, fileName);
+                                if (FindChild(newFileName) != null)
+                                {
+                                    // if we are doing 'Paste' and source file belongs to current project - generate fresh unique name
+                                    newFileName = GenerateCopyOfFileName(baseDir, fileName);
+                                }
                             }
                             else if (!IsContainedWithinProjectDirectory(file))
                             {