Declare range inclusion operators as taking anyelement not anynonarray.

Use of anynonarray was a crude hack to get around ambiguity versus the
array inclusion operators of the same names.  My previous patch to extend
the parser's type resolution heuristics makes that unnecessary, so use
the more general declaration instead.  This eliminates a wart that these
operators couldn't be used with ranges over arrays, which are otherwise
supported just fine.

Also, mark range_before and range_after as commutator operators,
per discussion with Jeff Davis.