Add support for 16 bit activations in ExpandDims operation. (#2589)

The change introduces the support for ML models with 16 bit activations and 8 bit weights in the ExpandDims operation.

BUG=fixes #68293

tensorflow/lite/micro/kernels/expand_dims.cc

diff --git a/tensorflow/lite/micro/kernels/expand_dims.cc b/tensorflow/lite/micro/kernels/expand_dims.cc
index 6bae37b..d47b42c 100644
--- a/tensorflow/lite/micro/kernels/expand_dims.cc
+++ b/tensorflow/lite/micro/kernels/expand_dims.cc
@@ -13,6 +13,8 @@
 limitations under the License.
 ==============================================================================*/
 
+#include <cstdint>
+
 #include "tensorflow/lite/c/common.h"
 #include "tensorflow/lite/kernels/internal/tensor_ctypes.h"
 #include "tensorflow/lite/kernels/kernel_util.h"
@@ -128,13 +130,18 @@
       memCopyN(tflite::micro::GetTensorData<float>(output),
                tflite::micro::GetTensorData<float>(input), flat_size);
     } break;
+    case kTfLiteInt16: {
+      memCopyN(tflite::micro::GetTensorData<int16_t>(output),
+               tflite::micro::GetTensorData<int16_t>(input), flat_size);
+    } break;
     case kTfLiteInt8: {
       memCopyN(tflite::micro::GetTensorData<int8_t>(output),
                tflite::micro::GetTensorData<int8_t>(input), flat_size);
     } break;
     default:
       MicroPrintf(
-          "Expand_Dims only currently supports int8 and float32, got %d.",
+          "Expand_Dims only currently supports int8, int16 and float32, got "
+          "%d.",
           input->type);
       return kTfLiteError;
   }

tensorflow/lite/micro/kernels/expand_dims_test.cc

diff --git a/tensorflow/lite/micro/kernels/expand_dims_test.cc b/tensorflow/lite/micro/kernels/expand_dims_test.cc
index d8e217e..39a83b5 100644
--- a/tensorflow/lite/micro/kernels/expand_dims_test.cc
+++ b/tensorflow/lite/micro/kernels/expand_dims_test.cc
@@ -13,6 +13,8 @@
 limitations under the License.
 ==============================================================================*/
 
+#include <cstdint>
+
 #include "tensorflow/lite/c/builtin_op_data.h"
 #include "tensorflow/lite/c/common.h"
 #include "tensorflow/lite/micro/kernels/kernel_runner.h"
@@ -138,6 +140,20 @@
                                           golden_data, output_data);
 }
 
+TF_LITE_MICRO_TEST(ExpandDimsPositiveAxisTest3) {
+  int16_t output_data[6];
+  int input_dims[] = {3, 3, 1, 2};
+  const int16_t input_data[] = {-1, 1, 2, -2, 0, 3};
+  const int16_t golden_data[] = {-1, 1, 2, -2, 0, 3};
+  int axis_dims[] = {1, 1};
+  const int32_t axis_data[] = {3};
+  int golden_dims[] = {1, 3, 1, 2};
+  int output_dims[] = {4, 3, 1, 2, 1};
+  tflite::testing::TestExpandDims<int16_t>(input_dims, input_data, axis_dims,
+                                           axis_data, golden_dims, output_dims,
+                                           golden_data, output_data);
+}
+
 TF_LITE_MICRO_TEST(ExpandDimsNegativeAxisTest4) {
   int8_t output_data[6];
   int input_dims[] = {3, 3, 1, 2};