Qualcomm AI Engine Direct - Add Unittest for Saver (pytorch#12325)

### Summary
- Add Unittest for Saver backend

### Test plan
```
python -m backends.qualcomm.tests.test_qnn_delegate TestQNNQuantizedUtils.test_qnn_backend_saver_backend -s ${device_id} -H ${host_id} -m ${soc} -b build-android
```

Author: DannyYuyang-quic

backends/qualcomm/qnn_preprocess.py

@@ -178,6 +178,11 @@ def preprocess_multimethod(
 
             if len(py_op_wrapper_list) == len(edge_programs.values()):
                 qnn_context_binary = qnn_manager.Compile(graph_name, py_op_wrapper_list)
+                if option.saver:
+                    # TODO: Currently, only the first method is saved. Update this logic if saving multiple methods becomes necessary in the future.
+                    exit(
+                        f"Record all QNN API calls from saver backend at: {option.saver_output_dir}"
+                    )
                 assert (
                     len(qnn_context_binary) != 0
                 ), "Failed to generate Qnn context binary."

backends/qualcomm/tests/test_qnn_delegate.py

@@ -3384,6 +3384,38 @@ def test_qnn_backend_rewrite_prepared_observer(self):
         quantized_module = convert_pt2e(prepared)
         self.lower_module_and_test_output(quantized_module, sample_input)
 
+    def test_qnn_backend_saver_backend(self):
+        backend_options = generate_htp_compiler_spec(use_fp16=False)
+        TestQNN.compiler_specs = generate_qnn_executorch_compiler_spec(
+            soc_model=self.chipset_table[TestQNN.model],
+            backend_options=backend_options,
+            saver=True,
+        )
+        module = Relu()  # noqa: F405
+        sample_input = (torch.randn([2, 5, 1, 3]),)
+        module = self.get_qdq_module(module, sample_input)
+
+        from executorch.backends.qualcomm.serialization.qc_schema_serialize import (
+            flatbuffer_to_option,
+            option_to_flatbuffer,
+        )
+
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            option = flatbuffer_to_option(TestQNN.compiler_specs[0].value)
+            option.saver_output_dir = f"{tmp_dir}/saver_output"
+            TestQNN.compiler_specs[0].value = option_to_flatbuffer(option)
+
+            with self.assertRaises(SystemExit):
+                self.lower_module_and_test_output(module, sample_input)
+            self.assertTrue(
+                os.path.isfile(f"{tmp_dir}/saver_output/params.bin"),
+                "failed to find params.bin",
+            )
+            self.assertTrue(
+                os.path.isfile(f"{tmp_dir}/saver_output/saver_output.c"),
+                "failed to find saver_output.c",
+            )
+
     def test_qnn_backend_skip_node_id_partitioner(self):
         module = SimpleModel()  # noqa: F405
         sample_input = (torch.ones(1, 32, 28, 28), torch.ones(1, 32, 28, 28))