Move some things to wxBitmapBase to avoid much duplication.

Use proper const for XPM data, and const void* for arbitary bitmap data.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41689 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/xpmdecod.h

@@ -35,7 +35,7 @@ public:
     wxImage ReadFile(wxInputStream& stream);
 #endif
     // Read directly from XPM data (as passed to wxBitmap ctor):
-    wxImage ReadData(const char **xpm_data);
+    wxImage ReadData(const char* const* xpm_data);
 };
 
 #endif // wxUSE_IMAGE && wxUSE_XPM