[ASTImporter] Support new AST nodes:
- UnresolvedUsingType
- EmptyDecl
- NamespaceAliasDecl
- UsingDecl
- UsingShadowDecl
- UsingDirectiveDecl
- UnresolvedUsingValueDecl
- UnresolvedUsingTypenameDecl
Refactor error handling in ImportTemplateArgumentLoc() method.
Add a test for inline namespaces.
llvm-svn: 318776