[build] Fix CMake protobuf dependency handling (#6772)

Reverts #6609 since that fix didn't Just Work(tm) on Windows. (edit: or Ubuntu. Seems to have broken everything except macOS.) This PR configures CMake to try and find protobuf-config.cmake first, which allows protobuf to pull in abseil for us. If protobuf-config.cmake is not available (coprocessors which don't have a new enough protobuf installed are a common case), it will fallback to CMake's built-in FindProtobuf module, which is what we were using before.

Add wpi::CreateMessage, a wrapper with an ifdef to switch between Arena::CreateMessage and Arena::Create, since the former is deprecated in newer versions of protobuf. This allows forward compatibility with newer versions of protobuf.

wpiutil/src/main/native/include/wpi/ProtoHelper.h

@@ -0,0 +1,18 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <google/protobuf/message.h>
+
+namespace wpi {
+template <typename T>
+inline T* CreateMessage(google::protobuf::Arena* arena) {
+#if GOOGLE_PROTOBUF_VERSION < 4000000
+  return google::protobuf::Arena::CreateMessage<T>(arena);
+#else
+  return google::protobuf::Arena::Create<T>(arena);
+#endif
+}
+}  // namespace wpi