W32: Add a mapping for "left_ptr_watch" cursor

This is purely to support gdk_cursor_new_from_name().
In particular, its counterpart, gdk_cursor_new_for_display(), will not
be affected, because there's no GDK_LEFT_PTR_WATCH cursor type,
and because i don't have a fallback cursor bitmask for gdk/win32/xcursors.h

gdk/win32/gdkcursor-win32.c

@@ -187,6 +187,7 @@ static struct {
 #endif
   { "help",  IDC_HELP },
   { "ibeam", IDC_IBEAM },
+  { "left_ptr_watch", IDC_APPSTARTING },
   { "sizeall", IDC_SIZEALL },
   { "sizenesw", IDC_SIZENESW },
   { "sizens", IDC_SIZENS },