Add aten::to NNAPI converter (#58540)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58540

Add support for aten::to op in the NNAPI model converter for simple
cases like to("cpu"), to("gpu")

Test Plan: pytest test/test_nnapi.py::TestNNAPI::test_to

Reviewed By: anshuljain1

Differential Revision: D28531941

fbshipit-source-id: 0c934f7aceaff2669307c3426efe32046d8c44f3

test/test_nnapi.py

@@ -238,6 +238,26 @@ class TestNNAPI(TestCase):
             convert_args=[torch.zeros(0, 0)],
         )
 
+    def test_to(self):
+        class ToCPU(torch.nn.Module):
+            def __init__(self):
+                super().__init__()
+                self.prelu = torch.nn.PReLU()
+
+            def forward(self, x):
+                y = x.to("cpu")
+                # add prelu since input operand can't be output
+                return self.prelu(y)
+
+        arg = torch.randn(1, 2, 3, 3)
+        self.check(ToCPU(), arg)
+        # Test flexible size
+        self.check(
+            ToCPU(),
+            arg,
+            convert_args=[torch.zeros(1, 2, 0, 0)],
+        )
+
     def test_mean(self):
         class MeanModule(torch.nn.Module):
             def __init__(self, dim, keep=False):