`Type.as_string` should not cause an error.

[fridis]

This was brought up in #3737: Type.as_string causes an error, even though it can be interpreted as a type feature call:

 > ./build/bin/fz -e "say Type.as_string"

command line:1:5: error 1: Feature not visible at call site
say Type.as_string

Feature not found: 'Type' (no arguments)
Target feature: 'universe'
In call: 'Type'
To solve this, you might change the visibility of the feature 'Type' (no arguments) at $MODULE/Type.fz:34:15:
module:public Type ref is


one error.

this works with .type

 > ./build/bin/fz -e "say Type.type.as_string"
Type of 'Type'

The visibility error shoud use the the pending error mechanism in Call.java to allow this.