[ASTImporter] Added visibility context check for TypedefNameDecl.

Summary:
ASTImporter makes now difference between typedefs and type aliases
with same name in different translation units
if these are not visible outside.

Reviewers: martong, a.sidorin, shafik, a_sidorin

Reviewed By: martong, shafik

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64480

llvm-svn: 370903