[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/cpp/protobuf/Protobuf.cpp

@@ -10,6 +10,7 @@
 #include <google/protobuf/io/zero_copy_stream.h>
 #include <google/protobuf/message.h>
 
+#include "wpi/ProtoHelper.h"
 #include "wpi/SmallVector.h"
 
 using namespace wpi;
@@ -170,7 +171,7 @@ static void ForEachProtobufDescriptorImpl(
                                   descproto);
   }
   if (!*descproto) {
-    *descproto = Arena::CreateMessage<FileDescriptorProto>(arena);
+    *descproto = wpi::CreateMessage<FileDescriptorProto>(arena);
   }
   (*descproto)->Clear();
   desc->CopyTo(*descproto);

wpiutil/src/main/native/cpp/protobuf/ProtobufMessageDatabase.cpp

@@ -6,6 +6,8 @@
 
 #include <google/protobuf/descriptor.h>
 
+#include "wpi/ProtoHelper.h"
+
 using namespace wpi;
 
 using google::protobuf::Arena;
@@ -34,7 +36,7 @@ bool ProtobufMessageDatabase::Add(std::string_view filename,
 
   if (!file.proto) {
     file.proto = std::unique_ptr<FileDescriptorProto>{
-        Arena::CreateMessage<FileDescriptorProto>(nullptr)};
+        wpi::CreateMessage<FileDescriptorProto>(nullptr)};
   } else {
     // replacing an existing one; remove any previously existing refs
     for (auto&& dep : file.proto->dependency()) {