Update on "Remove old QAT APIs"

**Summary:** As a follow-up to #2641,
which deprecated the old QAT APIs in 0.13.0, we remove them now
in the next release 0.15.0.

Fixes #2630.

**Test Plan:** CI

[ghstack-poisoned]

Author: andrewor14

torchao/utils.py

@@ -8,10 +8,11 @@
 import itertools
 import re
 import time
+import warnings
 from functools import reduce
 from importlib.metadata import version
 from math import gcd
-from typing import Any, Callable, Optional
+from typing import Any, Callable, Optional, Type
 
 import torch
 import torch.nn.utils.parametrize as parametrize
@@ -367,6 +368,25 @@ def torch_version_at_least(min_version):
     return parse_version(torch.__version__) >= parse_version(min_version)
 
 
+class _ConfigDeprecationWrapper:
+    """
+    A deprecation wrapper that directs users from a deprecated "config function"
+    (e.g. `int4_weight_only`) to the replacement config class.
+    """
+
+    def __init__(self, deprecated_name: str, config_cls: Type):
+        self.deprecated_name = deprecated_name
+        self.config_cls = config_cls
+
+    def __call__(self, *args, **kwargs):
+        warnings.warn(
+            f"`{self.deprecated_name}` is deprecated and will be removed in a future release. "
+            f"Please use `{self.config_cls.__name__}` instead. Example usage:\n"
+            f"    quantize_(model, {self.config_cls.__name__}(...))"
+        )
+        return self.config_cls(*args, **kwargs)
+
+
 """
 Helper function for implementing aten op or torch function dispatch
 and dispatching to these implementations.