Go: Improve two class names and add some helper predicates

[owen-mc]

trafficstars

This pull request introduces deprecations and enhancements to the Go QL library, focusing on improving the link between declarations and the things that have been declared. Key changes include the deprecation of BuiltinType and DeclaredType in favor of new replacements, the addition of new methods for going from type and field declarations to the type and fields that have been declared, and updates to tests.