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