Add a function to save a bitmap callable from debugger

This allows to dump a bitmap to a disk file in order to examine it
outside of the debugger when debugging.

Note that at least MSVC and gdb are not smart enough to allow calling
wxBitmap::SaveFile() directly.

src/common/bmpbase.cpp

@@ -25,6 +25,11 @@
     #include "wx/mstream.h"
 #endif
 
+extern bool wxDumpBitmap(const wxBitmap& bitmap, const char* path)
+{
+    return bitmap.SaveFile(path, wxBITMAP_TYPE_BMP);
+}
+
 // ----------------------------------------------------------------------------
 // wxVariant support
 // ----------------------------------------------------------------------------