Create the foundation for testing CoreML export for wheels (#9381)

### Summary
As part of #9019, this will
allow us to test CoreML support for wheels.

#### Why are we only selectively running the executor test? 

Our `macos-*-stable` runners do not have xcode, which is required to
build and run these tests. Only GitHub's `macos-*-xlarge` runners have
xcode. We currently run these CoreML tests on
[trunk](https://github.com/pytorch/executorch/blob/7c6d2f332861907391450974a481b6d8e04732ed/.github/workflows/trunk.yml#L444-L477),
which would be way too expensive to use GitHub's runner given the
frequency. So let's limit the runner tests to just the wheel jobs. I
will work with Test Infra to get Xcode into our runners.

### Test plan

* Wheel tests shouldn't change
* Test locally

```bash
$ GITHUB_WORKSPACE=$(dirname $(pwd)) REPOSITORY=$(basename $(pwd)) python .ci/scripts/wheel/test_macos.py
```

Author: jathu

.ci/scripts/test_model.sh

@@ -209,9 +209,14 @@ test_model_with_qnn() {
   EXPORTED_MODEL=$(find "./${EXPORT_SCRIPT}" -type f -name "${MODEL_NAME}*.pte" -print -quit)
 }
 
+# Run CoreML tests.
+#
+# @param should_test If true, build and test the model using the coreml_executor_runner.
 test_model_with_coreml() {
-  if [[ "${BUILD_TOOL}" == "buck2" ]]; then
-    echo "coreml doesn't support buck2."
+  local should_test="$1"
+
+  if [[ "${BUILD_TOOL}" != "cmake" ]]; then
+    echo "coreml only supports cmake."
     exit 1
   fi
 
@@ -229,6 +234,14 @@ test_model_with_coreml() {
     echo "No .pte file found"
     exit 1
   fi
+
+  # Run the model
+  if [ "${should_test}" = true ]; then
+    echo "Testing exported model with coreml_executor_runner..."
+    local out_dir=$(mktemp -d)
+    COREML_EXECUTOR_RUNNER_OUT_DIR="${out_dir}" examples/apple/coreml/scripts/build_executor_runner.sh
+    "${out_dir}/coreml_executor_runner" --model_path "${EXPORTED_MODEL}"
+  fi
 }
 
 test_model_with_mps() {
@@ -247,7 +260,11 @@ elif [[ "${BACKEND}" == *"qnn"* ]]; then
   fi
 elif [[ "${BACKEND}" == *"coreml"* ]]; then
   echo "Testing ${MODEL_NAME} with coreml..."
-  test_model_with_coreml
+  should_test_coreml=false
+  if [[ "${BACKEND}" == *"test"* ]]; then
+    should_test_coreml=true
+  fi
+  test_model_with_coreml "${should_test_coreml}"
   if [[ $? -eq 0 ]]; then
     prepare_artifacts_upload
   fi

.ci/scripts/wheel/test_macos.py

@@ -14,6 +14,12 @@
             test_base.ModelTest(
                 model=Model.Mv3,
                 backend=Backend.XnnpackQuantizationDelegation,
-            )
+            ),
+            # Enable this once CoreML is suppported out-of-the-box
+            # https://github.com/pytorch/executorch/issues/9019
+            # test_base.ModelTest(
+            #     model=Model.Mv3,
+            #     backend=Backend.CoreMlTest,
+            # )
         ]
     )

examples/apple/coreml/scripts/build_executor_runner.sh

@@ -77,4 +77,11 @@ XCODE_WORKSPACE_DIR_PATH="$EXAMPLES_COREML_DIR_PATH/executor_runner"
 XCODE_BUILD_DIR_PATH="$EXAMPLES_COREML_DIR_PATH/xcode-build"
 
 xcodebuild build -workspace "$XCODE_WORKSPACE_DIR_PATH/coreml_executor_runner.xcworkspace" -scheme coreml_executor_runner BUILD_DIR="$XCODE_BUILD_DIR_PATH"
-cp -f "$XCODE_BUILD_DIR_PATH/DEBUG/coreml_executor_runner" "$PWD"
+
+if [[ -z "${COREML_EXECUTOR_RUNNER_OUT_DIR:-}" ]]; then
+    COREML_EXECUTOR_RUNNER_OUT_DIR=$(pwd)
+elif [[ ! -d "${COREML_EXECUTOR_RUNNER_OUT_DIR}" ]]; then
+    mkdir -p "${COREML_EXECUTOR_RUNNER_OUT_DIR}"
+fi
+cp -f "$XCODE_BUILD_DIR_PATH/DEBUG/coreml_executor_runner" "${COREML_EXECUTOR_RUNNER_OUT_DIR}"
+echo "created ${COREML_EXECUTOR_RUNNER_OUT_DIR}/coreml_executor_runner"

examples/models/__init__.py

@@ -44,6 +44,7 @@ def __str__(self) -> str:
 
 class Backend(str, Enum):
     XnnpackQuantizationDelegation = "xnnpack-quantization-delegation"
+    CoreMlTest = "coreml-test"
 
     def __str__(self) -> str:
         return self.value