[ASTImporter] Fix corrupted RecordLayout caused by circular referenced fields

UnaryOperator(&)'s creation might need layout of some records
whose fields importation are still on fly, the layout is incorrectly
computed and cached. Clients relying on this will not work properly
or crash direclty (e.g StaticAnalyzer's MemRegion.cpp (calculateOffset)).

Use UnaryOperator::CreateEmpty() instead of UnaryOperator::Create()
to avoid this computation.

Fixes https://github.com/llvm/llvm-project/issues/64170

Reviewed By: aaron.ballman, balazske, shafik

Differential Revision: https://reviews.llvm.org/D156201