Update imports after QAT was moved out of prototype

Summary: pytorch/ao#1091 moved QAT out of
prototype in torchao. This is a BC-breaking change so torchtune
also needs to update its QAT imports. Additionally, after
pytorch/ao#987 we decided that QAT in
torchao will use module swaps to insert fake quantizes, so there
is no need to have a separate module swap quantizer, so this
commit removes the `*ModuleSwapQuantizer` option.

Test Plan:
pytest -m integration_test tests/recipes/test_qat_distributed.py should work

Author: andrewor14

torchtune/training/quantization.py

@@ -5,6 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 from typing import Callable, Optional
+from warnings import warn
 
 from torchtune.utils._import_guard import _USE_NEW_TENSOR_CORE_TILED_LAYOUT_API
 
@@ -18,22 +19,29 @@
     int8_dynamic_activation_int4_weight,
     quantize_,
 )
-from torchao.quantization.prototype.qat import (
-    disable_4w_fake_quant,
-    disable_8da4w_fake_quant,
-    enable_4w_fake_quant,
-    enable_8da4w_fake_quant,
-    Int4WeightOnlyQATQuantizer,
-    Int8DynActInt4WeightQATQuantizer,
-)
-from torchao.quantization.prototype.qat._module_swap_api import (
-    disable_4w_fake_quant_module_swap,
-    disable_8da4w_fake_quant_module_swap,
-    enable_4w_fake_quant_module_swap,
-    enable_8da4w_fake_quant_module_swap,
-    Int4WeightOnlyQATQuantizerModuleSwap,
-    Int8DynActInt4WeightQATQuantizerModuleSwap,
-)
+
+try:
+    # torchao 0.7+
+    from torchao.quantization.qat import (
+        Int4WeightOnlyQATQuantizer,
+        Int8DynActInt4WeightQATQuantizer,
+    )
+    from torchao.quantization.qat.linear import (
+        disable_4w_fake_quant,
+        disable_8da4w_fake_quant,
+        enable_4w_fake_quant,
+        enable_8da4w_fake_quant,
+    )
+except ImportError:
+    # torchao 0.6 and before
+    from torchao.quantization.prototype.qat import (
+        disable_4w_fake_quant,
+        disable_8da4w_fake_quant,
+        enable_4w_fake_quant,
+        enable_8da4w_fake_quant,
+        Int4WeightOnlyQATQuantizer,
+        Int8DynActInt4WeightQATQuantizer,
+    )
 
 
 __all__ = [
@@ -52,9 +60,9 @@
 _quantizer_mode_to_enable_fake_quant = {}
 
 
-# ========================================================
-# int8 dynamic activations + int4 weight tensor subclass |
-# ========================================================
+# ========================================
+# int8 dynamic activations + int4 weight |
+# ========================================
 
 
 class Int8DynActInt4WeightQuantizer:
@@ -106,15 +114,15 @@ def quantize(self, model):
 _quantizer_mode_to_enable_fake_quant["4w-qat"] = enable_4w_fake_quant
 
 
-# =============
-# module swap |
-# =============
+# ====================== #
+# Backward compatibility #
+# ====================== #
 
-# Note: QAT tensor subclass implementation in torchao only works
-# with FSDP2 today. For other distribution strategies like DDP and
-# FSDP1, users will need to fall back to the old module swap flow.
 
 # int4 weight-only
+Int4WeightOnlyQATQuantizerModuleSwap = Int4WeightOnlyQATQuantizer
+disable_4w_fake_quant_module_swap = disable_4w_fake_quant
+enable_4w_fake_quant_module_swap = enable_4w_fake_quant
 _quantizer_to_mode[Int4WeightOnlyQATQuantizerModuleSwap] = "4w-qat-module-swap"
 _quantizer_mode_to_disable_fake_quant[
     "4w-qat-module-swap"
@@ -124,6 +132,9 @@ def quantize(self, model):
 ] = enable_4w_fake_quant_module_swap
 
 # int8 dynamic activations + int4 weight
+Int8DynActInt4WeightQATQuantizerModuleSwap = Int8DynActInt4WeightQATQuantizer
+disable_8da4w_fake_quant_module_swap = disable_8da4w_fake_quant
+enable_8da4w_fake_quant_module_swap = enable_8da4w_fake_quant
 _quantizer_to_mode[Int8DynActInt4WeightQATQuantizerModuleSwap] = "8da4w-qat-module-swap"
 _quantizer_mode_to_disable_fake_quant[
     "8da4w-qat-module-swap"
@@ -142,15 +153,20 @@ def get_quantizer_mode(quantizer: Optional[Callable]) -> Optional[str]:
     Currently supported:
 
     - :class:`~torchao.quantization.quant_api.Int8DynActInt4WeightQuantizer`: "8da4w" (requires ``torch>=2.3.0``)
-    - :class:`~torchao.quantization.prototype.qat.Int8DynActInt4WeightQATQuantizer`: "8da4w-qat" (requires ``torch>=2.4.0``)
+    - :class:`~torchao.quantization.qat.Int8DynActInt4WeightQATQuantizer`: "8da4w-qat" (requires ``torch>=2.4.0``)
 
     Args:
         quantizer (Optional[Callable]): A callable object that implements the `quantize` method.
 
     Returns:
         Optional[str]: The quantization mode.
     """
-    return _quantizer_to_mode.get(type(quantizer), None)
+    mode = _quantizer_to_mode.get(type(quantizer), None)
+    if mode is not None and "module-swap" in mode:
+        warn(
+            "*QuantizerModuleSwap is deprecated. Please use the version without 'ModuleSwap' instead"
+        )
+    return mode
 
 
 def _get_disable_fake_quant(quantizer_mode: str) -> Callable: