Add a mechanism to print type names/strings in inline error messages without macros.

[jsuereth]

Simple Idea:

Add the following method to compiletime package akin to the following::

import scala.quoted._
private def showTypeImpl[T: Type](using Quotes): Expr[String] =
  Expr(Type.show[T])
/** Pulls a full-string (unique) name for the given type. */
inline def showType[T]: String = ${showTypeImpl[T]}

This could then be used in compiletime error messages like:

inline def myMethod[T]: Any =
    compiletime.error("myMethod not implemented for type: " + compiletime.showType[T])