Fix aten.div type promotion for FakeTensor (#150874)

Summary:
When we divide a FakeTensor by an integer using the fast op implementation, the type promotion should be `ELEMENTWISE_TYPE_PROMOTION_KIND.INT_TO_FLOAT` so we get a float when dividing an int FakeTensor by an integer.

```
FAST = get_fast_op_impls()
fast_div = FAST[torch.ops.aten.div.Tensor]
fast_div(fake_tensor, some_int)
```

Test Plan:
```
python test/test_fake_tensor.py -k test_fast_div
```

Differential Revision: D72667430

Pull Request resolved: https://github.com/pytorch/pytorch/pull/150874
Approved by: https://github.com/angelayi

test/test_fake_tensor.py

@@ -972,6 +972,14 @@ class FakeTensorTest(TestCase):
         self.assertIsInstance(r[0], FakeTensor)
         self.assertIsInstance(r[1], FakeTensor)
 
+    def test_fast_div(self):
+        mode = FakeTensorMode()
+        with mode:
+            x = torch.empty(2, 2, device="cpu", dtype=torch.int32)
+        from torch._subclasses.fake_impls import get_fast_op_impls
+        fast_div = get_fast_op_impls()[torch.ops.aten.div.Tensor]
+        y = fast_div(mode, x, 2)
+        self.assertEqual(y.dtype, torch.float32)
 
 instantiate_parametrized_tests(FakeTensorTest)
 

torch/_subclasses/fake_impls.py

@@ -890,7 +890,9 @@ def infer_size(a, b):
     return tuple(expandedSizes)
 
 
-def make_fast_binary_impl(slow_ref):
+def make_fast_binary_impl(
+    slow_ref, type_promotion_kind=ELEMENTWISE_TYPE_PROMOTION_KIND.DEFAULT
+):
     def fast_binary_impl(mode, *args, **kwargs):
         def slow(msg):
             count_label(f"slow {msg}")
@@ -957,7 +959,7 @@ def make_fast_binary_impl(slow_ref):
             # compute promotion
             # TODO: we don't need the compute type
             _, common_dtype = elementwise_dtypes(
-                *operands, type_promotion_kind=ELEMENTWISE_TYPE_PROMOTION_KIND.DEFAULT
+                *operands, type_promotion_kind=type_promotion_kind
             )
 
         # check all tensors on same device
@@ -1042,7 +1044,10 @@ def get_fast_op_impls():
     )
     register_fast_op_impl(torch.ops.aten.mul.Tensor)(make_fast_binary_impl(torch._refs.mul))  # type: ignore[has-type]
     register_fast_op_impl(torch.ops.aten.div.Tensor)(
-        make_fast_binary_impl(torch._refs.div)
+        make_fast_binary_impl(
+            torch._refs.div,
+            type_promotion_kind=ELEMENTWISE_TYPE_PROMOTION_KIND.INT_TO_FLOAT,
+        )
     )
     register_fast_op_impl(torch.ops.aten.detach.default)(fast_detach)
     return FAST_OP_IMPLEMENTATIONS