[3.13] Docs: Document `PyExceptionClass` functions in the C API (GH-135697) (GH-135758)

Docs: Document `PyExceptionClass` functions in the C API (GH-135697)

* Docs: Document `PyExceptionClass_Name`

`PyExceptionClass_Name` is an undocumented function in the limited API.

* Document `PyExceptionClass_Check`
(cherry picked from commit 59963e866a1bb8128a50cd53d1b13eeab03df06e)

Co-authored-by: Yuki Kobayashi <drsuaimqjgar@gmail.com>