Always use default margins for wxBitmapButton under Mac

Previously this was only done when wxBU_AUTODRAW was specified, making
this the only place in wxWidgets where this style was actually used.

This was not ideal, as the same code, not using wxBU_AUTODRAW, worked
just fine under MSW and GTK, but created ugly-looking buttons under Mac,
so do the right thing by default and let people call SetMargins(0, 0) if
they really don't want to have any margins.

Closes #18170.

docs/changes.txt

@@ -47,6 +47,10 @@ Changes in behaviour not resulting in compilation errors
   event handlers if you want the standard key combinations such as Alt-Space or
   Alt-F4 to work.
 
+- wxOSX port uses default button margins for wxBitmapButton by default, for
+  consistency with the other ports. You now need to call SetMargins(0, 0)
+  explicitly if you really don't want to have any margins in your buttons.
+
 
 Changes in behaviour which may result in build errors
 -----------------------------------------------------

src/osx/bmpbuttn_osx.cpp

@@ -38,16 +38,8 @@ bool wxBitmapButton::Create( wxWindow *parent,
                                      validator, name) )
         return false;
 
-    if ( style & wxBU_AUTODRAW )
-    {
-        m_marginX =
-        m_marginY = wxDEFAULT_BUTTON_MARGIN;
-    }
-    else
-    {
-        m_marginX =
-        m_marginY = 0;
-    }
+    m_marginX =
+    m_marginY = wxDEFAULT_BUTTON_MARGIN;
 
     m_bitmaps[State_Normal] = bitmap;