Refactor MTK build scripts Test building MTK examples and runners in ci (#13085)

### Summary
- Add building MTK examples to CI
- Separate MTK backend build script and example build script

Author: neuropilot-captain

.ci/scripts/build-mediatek-sdk.sh

@@ -14,9 +14,9 @@ build_neuron_backend() {
   export NEURON_BUFFER_ALLOCATOR_LIB=${MEDIATEK_SDK_ROOT}/libneuron_buffer_allocator.so
   export EXECUTORCH_ROOT="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/../.." && pwd)"
 
-
   cd ${EXECUTORCH_ROOT}
   ./backends/mediatek/scripts/mtk_build.sh
+  ./examples/mediatek/mtk_build_examples.sh
 }
 
 build_neuron_backend

backends/mediatek/scripts/mtk_build.sh

@@ -4,18 +4,20 @@
 set -e
 
 # Define the directory where CMakeLists.txt is located
-SOURCE_DIR=$(realpath "$(dirname "$0")/../../..")
+EXECUTORCH_ROOT=$(realpath "$(dirname "$0")/../../..")
+echo EXECUTORCH_ROOT=${EXECUTORCH_ROOT}
 
 # Check if the ANDROID_NDK environment variable is set
 if [ -z "$ANDROID_NDK" ]; then
     echo "Error: ANDROID_NDK environment variable is not set." >&2
     exit 1
 fi
 
-# Create and enter the build directory
+# Enter the build directory
+cd "$EXECUTORCH_ROOT"
+
 # Set build directory
 build_dir="cmake-android-out"
-cd "$SOURCE_DIR"
 rm -rf "${build_dir}"
 
 # Configure the project with CMake

examples/mediatek/README.md

@@ -28,6 +28,8 @@ examples/mediatek
 ## Environment Setup
 - Follow the instructions of **Prerequisites** and **Setup** in `backends/mediatek/scripts/README.md`.
 
+- Build required libraries by `backends/mediatek/scripts/mtk_build.sh` before building examples.
+
 ## Build MediaTek Examples
 1. Build the backend and the examples by exedcuting the script:
 ```bash

examples/mediatek/mtk_build_examples.sh

@@ -14,29 +14,18 @@ if [ -z "$ANDROID_NDK" ]; then
 fi
 
 main() {
-    # Set build directory
-    local build_dir="cmake-android-out"
-
-    # Create and enter the build directory
+    # Enter the build directory
     cd "$EXECUTORCH_ROOT"
-    rm -rf "${build_dir}"
-
-    # Configure the project with CMake
-    # Note: Add any additional configuration options you need here
-    cmake -DCMAKE_INSTALL_PREFIX="${build_dir}" \
-          -DCMAKE_TOOLCHAIN_FILE="$ANDROID_NDK/build/cmake/android.toolchain.cmake" \
-          -DANDROID_ABI=arm64-v8a \
-          -DANDROID_NATIVE_API_LEVEL=26 \
-          -DANDROID_PLATFORM=android-26 \
-          -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
-          -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
-          -DEXECUTORCH_BUILD_EXTENSION_FLAT_TENSOR=ON \
-          -DEXECUTORCH_BUILD_NEURON=ON \
-          -B"${build_dir}"
 
+    # Set build directory
+    local build_dir="cmake-android-out"
 
-    # Build the project
-    cmake --build "${build_dir}" --target install --config Release -j5
+    # Check if the build directory exists
+    if [ ! -d "$EXECUTORCH_ROOT/$build_dir" ]; then
+        echo "Error: Build directory '$build_dir' does not exist."
+        echo "Please build MTK backend before running this script."
+        exit 1
+    fi
 
     ## Build example
     local example_dir=examples/mediatek