[llvm] [C API] Add getters for Target Extension Types to C API (PR #71291)

[Joshua Cranmer via llvm-commits]

https://github.com/jcranmer-intel commented:

Looking at the other methods, I think it would also help to have a get I'th type/integer parameter method too in the API.

https://github.com/llvm/llvm-project/pull/71291