Generic way to access the underlying type of an UDVT

## Abstract

type().max min should work with user defined types that are mapped to scalar types

type MY_THING is uint32;
MY_THING constant MY_THIN_FLAG=type(uint32).max;

is what's currently required because I can't write type(MY_THING).max.

## Motivation

This is really unfortunate, as it destroys one of the main utilities of such a type alias. Now if I decide I want more bits for MY_THING I have to change the underlying type in multiple places = much larger probability of introducing a bug.

## Specification

Allow type(user_defined_type) when user_defined_type maps to a scalar underlying type.

## Backwards Compatibility

none

Start with the issue's UDVT examples and specification, then locate the compiler handling for type(...) and scalar user-defined value types. Done means type(MY_THING).max and type(MY_THING).min work for a UDVT mapped to a scalar type, with coverage for the uint32 example.

Written by the indexing model from the issue text.