[hop][BE] add util diff_meta with prettier error message. (#142162)

The error message changes from:
```python
-torch._dynamo.exc.Unsupported: Expected branches to return tensors with same metadata. [(tensor_pair, difference)...]:[('pair0:', TensorMetadata(shape=torch.Size([4, 3]), dtype=torch.float32, requires_grad=False, stride=(3, 1), memory_format=None, is_quantized=False, qparams={}), TensorMetadata(shape=torch.Size([2, 3]), dtype=torch.float32, requires_grad=False, stride=(3, 1), memory_format=None, is_quantized=False, qparams={}))]
```
to
```python
+torch._dynamo.exc.Unsupported: Expect branches to return tensors with same metadata but find pair[0] differ in 'shape', where lhs is TensorMetadata(shape=torch.Size([4, 3]), dtype=torch.float32, requires_grad=False, stride=(3, 1), memory_format=None, is_quantized=False, qparams={}) and rhs is TensorMetadata(shape=torch.Size([2, 3]), dtype=torch.float32, requires_grad=False, stride=(3, 1), memory_format=None, is_quantized=False, qparams={})
```

Pull Request resolved: https://github.com/pytorch/pytorch/pull/142162
Approved by: https://github.com/zou3519

test/dynamo/test_higher_order_ops.py

@@ -6957,6 +6957,23 @@ class ActivationCheckpointingTests(torch._dynamo.test_case.TestCase):
         with self.assertRaises(AssertionError):
             opt_test(True, False, inp)
 
+    def test_cond_with_mismatched_output(self):
+        def output_mismatch_test(x):
+            def true_fn():
+                return torch.concat([x, x])
+
+            def false_fn():
+                return x.sin()
+
+            return torch.cond(x.sum() > 0, true_fn, false_fn)
+
+        x = torch.randn(2, 3)
+        with self.assertRaises(torch._dynamo.exc.UncapturedHigherOrderOpError):
+            output_mismatch_test(x)
+
+        with self.assertRaises(torch._dynamo.exc.UncapturedHigherOrderOpError):
+            torch.compile(output_mismatch_test)(x)
+
     def test_non_aliasing_util(self):
         from torch._dynamo.variables.higher_order_ops import _assert_tensors_nonaliasing