Add DND move support on OS X

The drag mask passed by Cocoa is conservative and doesn't include
NSDragOperationMove which was added later. Override
draggingSourceOperationMaskForLocal to include that flag if it's wanted.

This also moving of text the default behaviour.

Closes #13819.
Closes #14726.

src/osx/cocoa/dnd.mm

@@ -56,11 +56,15 @@ wxDragResult NSDragOperationToWxDragResult(NSDragOperation code)
     BOOL dragFinished;
     int resultCode;
     wxDropSource* impl;
+
+    // Flags for drag and drop operations (wxDrag_* ).
+    int m_dragFlags;
 }
 
-- (void)setImplementation: (wxDropSource *)dropSource;
+- (void)setImplementation:(wxDropSource *)dropSource flags:(int)flags;
 - (BOOL)finished;
 - (NSDragOperation)code;
+- (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)forLocal;
 - (void)draggedImage:(NSImage *)anImage movedTo:(NSPoint)aPoint;
 - (void)draggedImage:(NSImage *)anImage endedAt:(NSPoint)aPoint operation:(NSDragOperation)operation;
 @end
@@ -73,12 +77,14 @@ wxDragResult NSDragOperationToWxDragResult(NSDragOperation code)
     dragFinished = NO;
     resultCode = NSDragOperationNone;
     impl = 0;
+    m_dragFlags = wxDrag_CopyOnly;
     return self;
 }
 
-- (void)setImplementation: (wxDropSource *)dropSource
+- (void)setImplementation:(wxDropSource *)dropSource flags:(int)flags
 {
     impl = dropSource;
+    m_dragFlags = flags;
 }
 
 - (BOOL)finished
@@ -91,6 +97,31 @@ wxDragResult NSDragOperationToWxDragResult(NSDragOperation code)
     return resultCode;
 }
 
+- (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)forLocal
+{
+    /*
+    By default drag targets receive a mask of NSDragOperationAll (0xf)
+    which, despite its name, does not include the later added
+    NSDragOperationMove (0x10) that sometimes is wanted.
+    Use NSDragOperationEvery instead because it includes all flags.
+
+    Note that this, compared to the previous behaviour, adds
+    NSDragOperationDelete to the mask which seems harmless.
+
+    We are also keeping NSDragOperationLink and NSDragOperationPrivate
+    in to preserve previous behaviour.
+    */
+
+    NSDragOperation allowedDragOperations = NSDragOperationEvery;
+
+    if (m_dragFlags == wxDrag_CopyOnly)
+    {
+        allowedDragOperations &= ~NSDragOperationMove;
+    }
+
+    return allowedDragOperations;
+}
+
 - (void)draggedImage:(NSImage *)anImage movedTo:(NSPoint)aPoint
 {
     wxUnusedVar( anImage );
@@ -186,7 +217,7 @@ wxDropSource* wxDropSource::GetCurrentDropSource()
     return gCurrentSource;
 }
 
-wxDragResult wxDropSource::DoDragDrop(int WXUNUSED(flags))
+wxDragResult wxDropSource::DoDragDrop(int flags)
 {
     wxASSERT_MSG( m_data, wxT("Drop source: no data") );
 
@@ -240,7 +271,7 @@ wxDragResult wxDropSource::DoDragDrop(int WXUNUSED(flags))
         
         
         DropSourceDelegate* delegate = [[DropSourceDelegate alloc] init];
-        [delegate setImplementation: this];
+        [delegate setImplementation:this flags:flags];
         [view dragImage:image at:p offset:NSMakeSize(0.0,0.0) 
             event: theEvent pasteboard: pboard source:delegate slideBack: NO];
         

src/osx/cocoa/window.mm

@@ -1210,6 +1210,11 @@ unsigned int wxOnDraggingEnteredOrUpdated(wxWidgetCocoaImpl* viewImpl,
     sourceDragMask contains copy, link, generic, and private flags. Formerly
     this would result in wxDragLink which is not what is expected for text.
     Give precedence to the move and copy flag instead.
+
+    TODO:
+    In order to respect wxDrag_DefaultMove, access to dnd.mm's
+    DropSourceDelegate will be needed which contains the wxDrag value used.
+    (The draggingSource method of sender points to a DropSourceDelegate* ).
     */
     wxDragResult result = wxDragNone;