Add wxMouseEvent::GetColumnsPerAction().

This is similar to the existing GetLinesPerAction() but is for, surprise,
columns.

Also change the documentation to say that the value returned by both of these
methods is 3 under "most platforms" as some wxOSX currently uses 1 and not 3.

Closes #15239.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74156 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -5607,7 +5607,20 @@ wxWindowMSW::HandleMouseWheel(wxMouseWheelAxis axis,
         }
     }
 
+    static int s_columnsPerRotation = -1;
+    if ( s_columnsPerRotation == -1 )
+    {
+        if ( !::SystemParametersInfo(SPI_GETWHEELSCROLLCHARS, 0,
+                                     &s_columnsPerRotation, 0))
+        {
+            // this setting is not supported on Windows 2000/XP, so use the value of 1
+            // http://msdn.microsoft.com/en-us/library/ms997498.aspx
+            s_columnsPerRotation = 1;
+        }
+    }
+
     event.m_linesPerAction = s_linesPerRotation;
+    event.m_columnsPerAction = s_columnsPerRotation;
     return HandleWindowEvent(event);
 
 #else // !wxUSE_MOUSEWHEEL