Add wxVersionInfo and functions returning it for 3rd party libraries.

Add simple wxVersionInfo class holding the version information.

Also add GetLibraryVersionInfo() static method to wx{JPEG,PNG,TIFF}Handler,
wxStyledTextCtrl and wxXmlDocument classes and wxGetZlibVersionInfo() and
wxGetLibraryVersionInfo() global functions using it.

Closes #12690.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66259 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/xml/xml.h

@@ -645,5 +645,13 @@ public:
         Deep copies the given document.
     */
     wxXmlDocument& operator=(const wxXmlDocument& doc);
+
+    /**
+       Get expat library version information.
+
+       @since 2.9.2
+       @see wxVersionInfo
+    */
+    static wxVersionInfo GetLibraryVersionInfo();
 };