Revert "remove dead proto_convert library (#97322)"

This reverts commit d850c33bfe3f1d1f0040738718cacb04ee449bdc.

Reverted https://github.com/pytorch/pytorch/pull/97322 on behalf of https://github.com/osalpekar due to This broke a large number of internal builds due to not being able to find proto_convert.h. See here: [D44319486](https://www.internalfb.com/diff/D44319486)

caffe2/utils/CMakeLists.txt

@@ -30,6 +30,7 @@ list(APPEND Caffe2_CPU_SRCS
   utils/math/utils.cc
   utils/math_cpu.cc
   utils/murmur_hash3.cc
+  utils/proto_convert.cc
   utils/proto_utils.cc
   utils/proto_wrap.cc
   utils/threadpool/ThreadPool.cc

caffe2/utils/proto_convert.cc

@@ -0,0 +1,5 @@
+#include "caffe2/utils/proto_convert.h"
+#include "caffe2/core/logging.h"
+
+namespace caffe2 {
+} // namespace caffe2

caffe2/utils/proto_convert.h

@@ -0,0 +1,11 @@
+#ifndef CAFFE2_UTILS_PROTO_CONVERT_H_
+#define CAFFE2_UTILS_PROTO_CONVERT_H_
+
+#include "caffe2/core/common.h"
+#include "caffe2/proto/caffe2_pb.h"
+#include "caffe2/proto/torch_pb.h"
+
+namespace caffe2 {
+} // namespace caffe2
+
+#endif // CAFFE2_UTILS_PROTO_CONVERT_H_