Add tsan_decr() API, counterpart of tsan_counter()
The existing tsan_counter() API increments a reference counter. Provide a new API, tsan_decr(), to decrement such a reference counter. This can be used, for example, when a reference is added to the session_ctx's sess_accept stats but should more properly be tracked in the regular ctx's statistics. Reviewed-by:Paul Dale <paul.dale@oracle.com> (Merged from https://github.com/openssl/openssl/pull/7464)