bpo-40602: Add _Py_HashPointerRaw() function (GH-20056)

Add a new _Py_HashPointerRaw() function which avoids replacing -1
with -2 to micro-optimize hash table using pointer keys: using
_Py_hashtable_hash_ptr() hash function.
diff --git a/Include/pyhash.h b/Include/pyhash.h
index 2f39858..4437b87 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -9,6 +9,8 @@
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(Py_hash_t) _Py_HashDouble(double);
 PyAPI_FUNC(Py_hash_t) _Py_HashPointer(const void*);
+// Similar to _Py_HashPointer(), but don't replace -1 with -2
+PyAPI_FUNC(Py_hash_t) _Py_HashPointerRaw(const void*);
 PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t);
 #endif