[SourceKit] Stub in a new "fully_annotated_decl" field to cursor info

This will eventually replace the existing annoteded_decl for cursor
info, and be added to doc info as well.  For now put in under a
different field name to not break existing clients.

For now, just reimplement the existing annotations but put in tag names
that are specific to the kind of type/decl. The goal is to fill in a
lot more substructure/detail over time.

Incidentally flesh out some cursor info tests.

rdar://problem/24292226

tools/SourceKit/include/SourceKit/Core/LangSupport.h

@@ -277,6 +277,9 @@ struct CursorInfo {
   StringRef GroupName;
   /// Annotated XML pretty printed declaration.
   StringRef AnnotatedDeclaration;
+  /// Fully annotated XML pretty printed declaration.
+  /// FIXME: this should eventually replace \c AnnotatedDeclaration.
+  StringRef FullyAnnotatedDeclaration;
   /// Non-empty if the symbol was imported from a clang module.
   StringRef ModuleName;
   /// Non-empty if a generated interface editor document has previously been