The simple parameters are those that successfully migrated to params.h
because they were trivial to declare in a way that could be used in all
the places where they are needed.

The PARAM() macro is now changed so that the outstanding `type` argument
is separated from arguments matching struct parspec fields. To minimize
disruption the new PARAM_SIMPLE() macro takes parameters in the order of
the previous PARAM() definition.

Refs #3250