[ASTImporter] Use llvm::Expected and Error in the importer API
This is the final phase of the refactoring towards using llvm::Expected
and llvm::Error in the ASTImporter API.
This involves the following:
- remove old Import functions which returned with a pointer,
- use the Import_New functions (which return with Err or Expected) everywhere and handle their return value
- rename Import_New functions to Import
This affects both Clang and LLDB.
Reviewers: shafik, teemperor, aprantl, a_sidorin, balazske, a.sidorin
Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits, lldb-commits
Tags: #clang, #lldb
Differential Revision: https://reviews.llvm.org/D61438