[clang] [clang][ASTImporter] Fix crash when template class static member imported to other translation unit. (PR #68774)

[Ding Fei via cfe-commits]

danix800 wrote:

Caused by missing `MemberSpecializationInfo` when importing so moving testcase into `ASTImporterTest` as unittest would be better.

https://github.com/llvm/llvm-project/pull/68774