UI: Use busyButClickableCursor for MacOS Wait Cursor

MacOS is currently using one of our custom "hourglass" cursors during
busy times. This PR changes it to an OS-supplied cursor, a pointer
arrow with an animated blue spinner, meant for this purpose. Although
undocumented it has been used by many applications for many years.
Including Firefox for 11 years now.

Pull Request: https://projects.blender.org/blender/blender/pulls/136735

intern/ghost/intern/GHOST_WindowCocoa.mm

@@ -1003,6 +1003,12 @@ static NSCursor *getImageCursor(GHOST_TStandardCursor shape, NSString *name, NSP
   return cursors[index];
 }
 
+/* busyButClickableCursor is an undocumented NSCursor API, but
+ * has been in use since at least OS X 10.4 and through 10.9. */
+@interface NSCursor (Undocumented)
++ (NSCursor *)busyButClickableCursor;
+@end
+
 NSCursor *GHOST_WindowCocoa::getStandardCursor(GHOST_TStandardCursor shape) const
 {
   @autoreleasepool {
@@ -1046,6 +1052,11 @@ NSCursor *GHOST_WindowCocoa::getStandardCursor(GHOST_TStandardCursor shape) cons
         return [NSCursor pointingHandCursor];
       case GHOST_kStandardCursorDefault:
         return [NSCursor arrowCursor];
+      case GHOST_kStandardCursorWait:
+        if ([NSCursor respondsToSelector:@selector(busyButClickableCursor)]) {
+          return [NSCursor busyButClickableCursor];
+        }
+        return nullptr;
       case GHOST_kStandardCursorKnife:
         return getImageCursor(shape, @"knife.pdf", NSMakePoint(6, 24));
       case GHOST_kStandardCursorEraser: