Invalidate best size when the bitmap or bitmap position changes. Add GetBitmapMargins

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63595 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/button.h

@@ -109,7 +109,8 @@ public:
     // set the margins around the image
     void SetBitmapMargins(wxCoord x, wxCoord y) { DoSetBitmapMargins(x, y); }
     void SetBitmapMargins(const wxSize& sz) { DoSetBitmapMargins(sz.x, sz.y); }
-
+    wxSize GetBitmapMargins() { return DoGetBitmapMargins(); }
+    
     // set the image position relative to the text, i.e. wxLEFT means that the
     // image is to the left of the text (this is the default)
     void SetBitmapPosition(wxDirection dir);