Add back mistakenly deleted QAT BC import test

Summary: The unused imports in this test were mistakenly deleted
in #1359. This commit adds
them back.

Test Plan:
python test/quantization/test_qat.py

Author: andrewor14

test/quantization/test_qat.py

@@ -1108,6 +1108,53 @@ def test_qat_prototype_bc(self):
         Just to make sure we can import all the old prototype paths.
         We will remove this test in the near future when we actually break BC.
         """
+        from torchao.quantization.prototype.qat import (
+            disable_4w_fake_quant,
+            disable_8da4w_fake_quant,
+            enable_4w_fake_quant,
+            enable_8da4w_fake_quant,
+            ComposableQATQuantizer,
+            Int8DynActInt4WeightQATLinear,
+            Int4WeightOnlyEmbeddingQATQuantizer,
+            Int4WeightOnlyQATQuantizer,
+            Int8DynActInt4WeightQATQuantizer,
+        )
+        from torchao.quantization.prototype.qat._module_swap_api import (
+            disable_4w_fake_quant_module_swap,
+            enable_4w_fake_quant_module_swap,
+            disable_8da4w_fake_quant_module_swap,
+            enable_8da4w_fake_quant_module_swap,
+            Int4WeightOnlyQATQuantizerModuleSwap,
+            Int8DynActInt4WeightQATQuantizerModuleSwap,
+        )
+        from torchao.quantization.prototype.qat.affine_fake_quantized_tensor import (
+            AffineFakeQuantizedTensor,
+            to_affine_fake_quantized,
+        )
+        from torchao.quantization.prototype.qat.api import (
+            ComposableQATQuantizer,
+            FakeQuantizeConfig,
+        )
+        from torchao.quantization.prototype.qat.embedding import (
+            FakeQuantizedEmbedding,
+            Int4WeightOnlyEmbeddingQATQuantizer,
+            Int4WeightOnlyEmbedding,
+            Int4WeightOnlyQATEmbedding,
+        )
+        from torchao.quantization.prototype.qat.fake_quantizer import (
+            FakeQuantizer,
+        )
+        from torchao.quantization.prototype.qat.linear import (
+            disable_4w_fake_quant,
+            disable_8da4w_fake_quant,
+            enable_4w_fake_quant,
+            enable_8da4w_fake_quant,
+            FakeQuantizedLinear,
+            Int4WeightOnlyQATLinear,
+            Int4WeightOnlyQATQuantizer,
+            Int8DynActInt4WeightQATLinear,
+            Int8DynActInt4WeightQATQuantizer,
+        )
 
 
 if __name__ == "__main__":