Add support for asserting JSON

Based on the JSONassert library.

Issue: SPR-10113
Expose handled exception as request attribute

This change exposes exceptions handled in the DispatcherServlet with a
HandlerExceptionResolver as a request attribute. This is done only when
the resolver returns an empty ModelAndView indicating the exception was
resolved but not view is required (e.g. status code was set). In such
cases the exception may be useful to any handlers in an ERRPR dispatch
by the servlet container.

Issue: SPR-11686