Single code path for type checking on a parameter in a built-in sub or method

[masak]

We do oodles of these right now in Builtins.pm:

            die X::TypeCheck.new(:operation<->, :got($lhs), :expected(_007::Object))
                unless $lhs ~~ _007::Object && $lhs.isa("Int");

We could extract that into an internal API so we can do

assertType(:value($lhs), :type<Int>, :operation<->);

instead. Could also consider whether it'd be a useful primitive to provide in 007 itself, given that core 007 doesn't have typed variables and parameters.