[wpiutil] Change C++ protobuf to nanopb (#7309)

The Google C++ protobuf implementation has issues with dynamic linkage across DLL boundaries because it uses global variables.  It also has a compile-time dependency because the protoc version must exactly match the libprotobuf version.  Using nanopb with a customized generator fixes both of these issues.

Co-authored-by: Gold856 <117957790+Gold856@users.noreply.github.com>

wpiutil/src/test/native/cpp/proto/TestProtoInner.h

@@ -0,0 +1,24 @@
+// 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 <wpi/protobuf/Protobuf.h>
+
+#include <string>
+
+#include "wpiutil.npb.h"
+
+struct TestProtoInner {
+  std::string msg;
+};
+
+template <>
+struct wpi::Protobuf<TestProtoInner> {
+  using MessageStruct = wpi_proto_TestProtoInner;
+  using InputStream = wpi::ProtoInputStream<TestProtoInner>;
+  using OutputStream = wpi::ProtoOutputStream<TestProtoInner>;
+  static std::optional<TestProtoInner> Unpack(InputStream& stream);
+  static bool Pack(OutputStream& stream, const TestProtoInner& value);
+};