[llvm] [Windows] Export Registry<T> members and accessors for plugins again (PR #221296)

[via llvm-commits]

serge-sans-paille wrote:

Thanks for the patch. I'm a bit worried that our CI did not detect that. We could at least detect an empty dynamic symbol table, at best try to link a plugin.

Do you feel you could craft one of those as part of this PR? I feel like `clang/lib/Analysis/plugins/CMakeLists.txt` should have caught this, but I haven't dug too far (yet)

https://github.com/llvm/llvm-project/pull/221296