[TypeSystem] Handle Clang AttributedTypes

When parsing types originating in modules, it is possible to encounter AttributedTypes 
(such as the type generated for NSString *_Nonnull). Some of LLDB's ClangASTContext 
methods deal with them; others do not. In particular, one function that did not was 
GetTypeInfo, causing TestObjCNewSyntax to fail.

This fixes that, treating AttributedType as essentially transparent and getting the 
information for the modified type.

In addition, however, TestObjCNewSyntax is a monolithic test that verifies a bunch of 
different things, all of which can break independently of one another. I broke it 
apart into smaller tests so that we get more precise failures when something (like 
this) breaks.

Differential Revision: https://reviews.llvm.org/D33812

llvm-svn: 304510