[clang] [clang][AST] Fix source range of class template implicit instantiations. (PR #156011)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

I have no idea. I just saw this branch was forced pushed, and current changes in this PR seems unrelated to discussion, so I want to  remind you.

https://github.com/llvm/llvm-project/pull/156011