Add wxCursor ctor from XPM data to all ports

This just uses the existing wxImage ctor from XPM data and wxCursor ctor
from wxImage, but will allow the code creating cursors from XPM to still
work even when wxImage ctor from XPM is made explicit.

Add a trivial test just to check that the new ctor can be used.

interface/wx/cursor.h

@@ -190,6 +190,17 @@ public:
     */
     wxCursor(const wxImage& image);
 
+    /**
+        Constructs a cursor from XPM data.
+
+        In versions of wxWidgets until 3.1.6 constructing wxCursor from XPM
+        data implicitly used wxImage constructor from XPM data and wxCursor
+        constructor from wxImage. Since 3.1.6 this constructor overload is
+        available to allow constructing wxCursor from XPM to still work, even
+        though wxImage constructor from XPM is now @c explicit.
+     */
+    wxCursor(const char* const* xpmData);
+
     /**
         Copy constructor, uses @ref overview_refcount "reference counting".