logic: improved indexer coverage for using decls, using directives

* moved source code for solving names of NestedNameSpecifiers to new CxxSpecifierNameResolver.
* implemented recording of UsingDirectives.
* implemented using file as context for using directives and using directive decls if no other context is available.
* re-implemented recording of the auto keyword

src/lib_cxx/data/parser/cxx/name_resolver/CxxDeclNameResolver.h

@@ -16,6 +16,7 @@ public:
 
 private:
 	NameHierarchy getContextNameHierarchy(const clang::DeclContext* declaration);
+	NameHierarchy getContextNameHierarchy(const clang::NestedNameSpecifier* specifier);
 	std::shared_ptr<NameElement> getDeclName(const clang::NamedDecl* declaration);
 	std::shared_ptr<NameElement> getNameForAnonymousSymbol(const std::string& symbolKindName, const clang::PresumedLoc& presumedBegin);
 	std::string getTemplateParameterString(const clang::NamedDecl* parameter);